build: only define WITH_POLKIT if enabled

configure.ac

@@ -296,9 +296,7 @@ elif test "x$with_polkit" = "xyes"; then
     with_polkit=strict
 fi
 
-if test "x$with_polkit" = "xno"; then
-    AC_DEFINE(WITH_POLKIT, 0, [Define if you have PolicyKit support])
-else
+if test "x$with_polkit" != "xno"; then
 	if test "x$have_polkit" = "xno"; then
 		AC_MSG_ERROR(PolicyKit development headers are required)
 	fi

src/mm-auth.c

@@ -21,8 +21,8 @@
 #include "mm-auth.h"
 #include "mm-auth-provider.h"
 
-#ifdef WITH_POLKIT
-#include "mm-auth-provider-polkit.h"
+#if defined WITH_POLKIT
+# include "mm-auth-provider-polkit.h"
 #endif
 
 static MMAuthProvider *authp = NULL;
@@ -31,7 +31,7 @@ MMAuthProvider *
 mm_auth_get_provider (void)
 {
     if (!authp) {
-#if WITH_POLKIT
+#if defined WITH_POLKIT
         authp = mm_auth_provider_polkit_new ();
 #else
         authp = mm_auth_provider_new ();