Hide U flag altogether if not on Linux

Signed-off-by: Tin Švagelj <tin.svagelj@live.com>

doc/man.md.j2

@@ -162,7 +162,8 @@ file.
 
 **-U \| \--unique**
 
-:   Conky won't start if another Conky process is already running.
+:   Conky won't start if another Conky process is already running. Implemented
+    only for Linux.
 
 **-v \| -V \| \--version** 
 

src/conky.cc

@@ -2106,7 +2106,10 @@ void set_current_config() {
 
 /* : means that character before that takes an argument */
 const char *getopt_string =
-    "vVqdDSs:t:u:i:hc:p:U"
+    "vVqdDSs:t:u:i:hc:p:"
+#if defined(__linux__)
+    "U"
+#endif
 #ifdef BUILD_X11
     "x:y:w:a:X:m:f:"
 #ifdef OWN_WINDOW
@@ -2136,8 +2139,12 @@ const struct option longopts[] = {
     {"double-buffer", 0, nullptr, 'b'}, {"window-id", 1, nullptr, 'w'},
 #endif /* BUILD_X11 */
     {"text", 1, nullptr, 't'},          {"interval", 1, nullptr, 'u'},
-    {"pause", 1, nullptr, 'p'},         {"unique", 0, nullptr, 'U'},
-    {nullptr, 0, nullptr, 0}};
+    {"pause", 1, nullptr, 'p'},
+#if defined(__linux__)
+    {"unique", 0, nullptr, 'U'},
+#endif /* Linux */
+    {nullptr, 0, nullptr, 0}
+};
 
 void setup_inotify() {
 #ifdef HAVE_SYS_INOTIFY_H

src/main.cc

@@ -275,6 +275,7 @@ static void print_help(const char *prog_name) {
          prog_name);
 }
 
+#if defined(__linux__)
 // NOTE: Only works on systems where there is a /proc/[pid]/stat file.
 static bool is_conky_already_running() {
   DIR *dir;
@@ -312,6 +313,7 @@ static bool is_conky_already_running() {
   closedir(dir);
   return instances > 1;
 }
+#endif /* Linux */
 
 inline void reset_optind() {
 #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || \
@@ -392,19 +394,22 @@ int main(int argc, char **argv) {
         window.window = strtol(optarg, nullptr, 0);
         break;
 #endif /* BUILD_X11 */
+#if defined(__linux__)
       case 'U':
         unique_process = true;
         break;
-
+#endif /* Linux */
       case '?':
         return EXIT_FAILURE;
     }
   }
 
+#if defined(__linux__)
   if (unique_process && is_conky_already_running()) {
     NORM_ERR("already running");
     return 0;
   }
+#endif /* Linux */
 
   try {
     set_current_config();