build: fix -Wunused-but-set-variable support and handle clang better

By default the build used -Wno-unused-but-set-variable but that's
clearly not what we want. Fix those problems.

When using clang, the compiler doesn't error on unknown compile
options, so let's add -Werror to the checking too.

CC='clang'
configure:3408: checking for gcc
configure:3435: result: clang
...
configure:17644: checking whether gcc understands -Wno-unused-but-set-variable
configure:17657: clang -c -Wall -std=gnu89 -g -O2 -Wmissing-declarations -Wmissing-prototypes -Wdeclaration-after-statement -Wstrict-prototypes -Wno-unused-parameter -Wno-sign-compare -Wno-deprecated-declarations -Wno-unused-but-set-variable  conftest.c >&5
warning: unknown warning option '-Wno-unused-but-set-variable'; did you mean '-Wno-unused-const-variable'? [-Wunknown-warning-option]
1 warning generated.
configure:17657: $? = 0
configure:17666: result: yes

Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>

m4/compiler_warnings.m4

@@ -11,9 +11,9 @@ if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
 		      -Wdeclaration-after-statement -Wstrict-prototypes \
 		      -Wno-unused-parameter -Wno-sign-compare \
 		      -Wno-deprecated-declarations \
-		      -Wno-unused-but-set-variable -Wformat-security; do
+		      -Wunused-but-set-variable -Wformat-security; do
 		SAVE_CFLAGS="$CFLAGS"
-		CFLAGS="$CFLAGS $option"
+		CFLAGS="$CFLAGS $option -Werror"
 		AC_MSG_CHECKING([whether gcc understands $option])
 		AC_TRY_COMPILE([], [],
 			has_option=yes,

src/mm-broadband-bearer.c

@@ -261,10 +261,8 @@ dial_cdma_ready (MMBaseModem *modem,
 static void
 cdma_connect_context_dial (GTask *task)
 {
-    MMBroadbandBearer      *self;
     DetailedConnectContext *ctx;
 
-    self = g_task_get_source_object (task);
     ctx = g_task_get_task_data (task);
 
     mm_base_modem_at_command_full (ctx->modem,

src/mm-broadband-modem-mbim.c

@@ -238,14 +238,16 @@ modem_load_current_capabilities_finish (MMIfaceModem *self,
 static void
 complete_current_capabilities (GTask *task)
 {
-    MMBroadbandModemMbim           *self;
     LoadCurrentCapabilitiesContext *ctx;
     MMModemCapability               result = 0;
 
-    self = g_task_get_source_object (task);
     ctx  = g_task_get_task_data (task);
 
 #if defined WITH_QMI && QMI_MBIM_QMUX_SUPPORTED
+    {
+        MMBroadbandModemMbim *self;
+
+        self = g_task_get_source_object (task);
         /* Warn if the MBIM loaded capabilities isn't a subset of the QMI loaded ones */
         if (ctx->current_qmi && ctx->current_mbim) {
             gchar *mbim_caps_str;
@@ -276,6 +278,7 @@ complete_current_capabilities (GTask *task)
          * don't mix both logics */
         if (self->priv->qmi_capability_and_mode_switching)
             mm_info ("QMI-based capability and mode switching support enabled");
+    }
 #else
     result = ctx->current_mbim;
 #endif
@@ -1967,9 +1970,7 @@ static void
 allocate_next_qmi_client (GTask *task)
 {
     InitializationStartedContext *ctx;
-    MMBroadbandModemMbim         *self;
 
-    self = g_task_get_source_object (task);
     ctx = g_task_get_task_data (task);
 
     if (ctx->qmi_service_index == G_N_ELEMENTS (qmi_services)) {
@@ -2608,12 +2609,9 @@ set_lte_attach_configuration_set_ready (MbimDevice   *device,
                                         GAsyncResult *res,
                                         GTask        *task)
 {
-    MMBroadbandModemMbim *self;
     MbimMessage          *response;
     GError               *error = NULL;
 
-    self = g_task_get_source_object (task);
-
     response = mbim_device_command_finish (device, res, &error);
     if (!response || !mbim_message_response_get_result (response, MBIM_MESSAGE_TYPE_COMMAND_DONE, &error))
         g_task_return_error (task, error);
@@ -2630,7 +2628,6 @@ before_set_lte_attach_configuration_query_ready (MbimDevice   *device,
                                                  GAsyncResult *res,
                                                  GTask        *task)
 {
-    MMBroadbandModemMbim        *self;
     MbimMessage                 *request;
     MbimMessage                 *response;
     GError                      *error = NULL;
@@ -2639,7 +2636,6 @@ before_set_lte_attach_configuration_query_ready (MbimDevice   *device,
     MbimLteAttachConfiguration **configurations = NULL;
     guint                        i;
 
-    self   = g_task_get_source_object (task);
     config = g_task_get_task_data (task);
 
     response = mbim_device_command_finish (device, res, &error);

src/mm-port-probe.c

@@ -1676,29 +1676,29 @@ MMPortType
 mm_port_probe_get_port_type (MMPortProbe *self)
 {
     const gchar *subsys;
-    const gchar *name;
 
     g_return_val_if_fail (MM_IS_PORT_PROBE (self), FALSE);
 
     subsys = mm_kernel_device_get_subsystem (self->priv->port);
-    name = mm_kernel_device_get_name (self->priv->port);
 
     if (g_str_equal (subsys, "net"))
         return MM_PORT_TYPE_NET;
 
+    if (g_str_has_prefix (subsys, "usb")) {
+        const gchar *name;
+
+        name = mm_kernel_device_get_name (self->priv->port);
+        if (g_str_has_prefix (name, "cdc-wdm")) {
 #if defined WITH_QMI
-    if (g_str_has_prefix (subsys, "usb") &&
+            if (self->priv->is_qmi)
-        g_str_has_prefix (name, "cdc-wdm") &&
-        self->priv->is_qmi)
                 return MM_PORT_TYPE_QMI;
 #endif
-
 #if defined WITH_MBIM
-    if (g_str_has_prefix (subsys, "usb") &&
+            if (self->priv->is_mbim)
-        g_str_has_prefix (name, "cdc-wdm") &&
-        self->priv->is_mbim)
                 return MM_PORT_TYPE_MBIM;
 #endif
+        }
+    }
 
     if (self->priv->flags & MM_PORT_PROBE_QCDM &&
         self->priv->is_qcdm)

src/mm-shared-qmi.c

@@ -398,14 +398,10 @@ out:
 static void
 set_current_capabilities_system_selection_preference (GTask *task)
 {
-    MMSharedQmi                                    *self;
-    Private                                        *priv;
     SetCurrentCapabilitiesContext                  *ctx;
     QmiMessageNasSetSystemSelectionPreferenceInput *input;
     QmiNasRatModePreference                         pref;
 
-    self = g_task_get_source_object (task);
-    priv = get_private (MM_SHARED_QMI (self));
     ctx  = g_task_get_task_data (task);
 
     pref = mm_modem_capability_to_qmi_rat_mode_preference (ctx->capabilities);
@@ -919,12 +915,9 @@ set_current_modes_technology_preference_ready (QmiClientNas *client,
                                                GAsyncResult *res,
                                                GTask        *task)
 {
-    SetCurrentModesContext                     *ctx;
     QmiMessageNasSetTechnologyPreferenceOutput *output = NULL;
     GError                                     *error = NULL;
 
-    ctx = g_task_get_task_data (task);
-
     output = qmi_client_nas_set_technology_preference_finish (client, res, &error);
     if (!output ||
         (!qmi_message_nas_set_technology_preference_output_get_result (output, &error) &&
@@ -993,12 +986,9 @@ set_current_modes_system_selection_preference_ready (QmiClientNas *client,
                                                      GAsyncResult *res,
                                                      GTask        *task)
 {
-    SetCurrentModesContext                          *ctx;
     QmiMessageNasSetSystemSelectionPreferenceOutput *output = NULL;
     GError                                          *error = NULL;
 
-    ctx = g_task_get_task_data (task);
-
     output = qmi_client_nas_set_system_selection_preference_finish (client, res, &error);
     if (!output || !qmi_message_nas_set_system_selection_preference_output_get_result (output, &error))
         g_task_return_error (task, error);
@@ -1016,11 +1006,9 @@ set_current_modes_system_selection_preference (GTask *task)
     MMIfaceModem                                   *self;
     SetCurrentModesContext                         *ctx;
     QmiMessageNasSetSystemSelectionPreferenceInput *input;
-    Private                                        *priv;
     QmiNasRatModePreference                         pref;
 
     self = g_task_get_source_object (task);
-    priv = get_private (MM_SHARED_QMI (self));
     ctx  = g_task_get_task_data (task);
 
     input = qmi_message_nas_set_system_selection_preference_input_new ();
@@ -1162,15 +1150,12 @@ get_technology_preference_ready (QmiClientNas *client,
                                  GAsyncResult *res,
                                  GTask        *task)
 {
-    LoadCurrentModesContext                    *ctx;
     LoadCurrentModesResult                     *result = NULL;
     QmiMessageNasGetTechnologyPreferenceOutput *output = NULL;
     GError                                     *error = NULL;
     MMModemMode                                 allowed;
     QmiNasRadioTechnologyPreference             preference_mask;
 
-    ctx = g_task_get_task_data (task);
-
     output = qmi_client_nas_get_technology_preference_finish (client, res, &error);
     if (!output || !qmi_message_nas_get_technology_preference_output_get_result (output, &error)) {
         g_task_return_error (task, error);
@@ -1226,15 +1211,12 @@ load_current_modes_system_selection_preference_ready (QmiClientNas *client,
                                                       GAsyncResult *res,
                                                       GTask        *task)
 {
-    LoadCurrentModesContext                         *ctx;
     LoadCurrentModesResult                          *result = NULL;
     QmiMessageNasGetSystemSelectionPreferenceOutput *output = NULL;
     GError                                          *error = NULL;
     QmiNasRatModePreference                          mode_preference_mask = 0;
     MMModemMode                                      allowed;
 
-    ctx = g_task_get_task_data (task);
-
     output = qmi_client_nas_get_system_selection_preference_finish (client, res, &error);
     if (!output || !qmi_message_nas_get_system_selection_preference_output_get_result (output, &error)) {
         g_task_return_error (task, error);
@@ -4068,7 +4050,6 @@ pds_get_default_tracking_session_ready (QmiClientPds *client,
                                         GAsyncResult *res,
                                         GTask        *task)
 {
-    MMSharedQmi                                  *self;
     SetGpsOperationModeContext                   *ctx;
     QmiMessagePdsSetDefaultTrackingSessionInput  *input;
     QmiMessagePdsGetDefaultTrackingSessionOutput *output;
@@ -4094,7 +4075,6 @@ pds_get_default_tracking_session_ready (QmiClientPds *client,
         return;
     }
 
-    self = g_task_get_source_object (task);
     ctx  = g_task_get_task_data (task);
 
     qmi_message_pds_get_default_tracking_session_output_get_info (