Bug 1357988 - Don't use IPC macros for media pref defaults. r=alfredo

MozReview-Commit-ID: 5b7YBewT52a

--HG--
extra : rebase_source : 5e7750ca38a8ca971655b347c3ac1c3a02a3df0b

dom/media/MediaPrefs.h

@@ -175,7 +175,7 @@ private:
   DECL_MEDIA_PREF("media.rust.test_mode",                     RustTestMode, bool, false);
 #endif
 
-#if defined(OS_LINUX)
+#if defined(MOZ_WIDGET_GTK)
   DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, true);
 #else
   DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, false);