Fix compilation error after recent changes to strict gcc flags

Dudes, please try building blender with all default features
before doing such a commits. It helps just a lot when bisecting
issues later.

Also solved const qualifier discard happens in recent monofont
commit.

source/blender/blenfont/intern/blf_translation.c

@@ -94,7 +94,7 @@ unsigned char *BLF_get_unifont_mono(int *unifont_size_r)
 {
 #ifdef WITH_INTERNATIONAL
 	if(unifont_mono_ttf == NULL) {
-		char *fontpath = BLI_get_folder(BLENDER_DATAFILES, "fonts");
+		const char *fontpath = BLI_get_folder(BLENDER_DATAFILES, "fonts");
 		if (fontpath) {
 			char unifont_path[1024];
 

source/blender/blenkernel/intern/writeffmpeg.c

@@ -981,7 +981,6 @@ int BKE_ffmpeg_start(struct Scene *scene, RenderData *rd, int rectx, int recty,
 	return success;
 }
 
-void BKE_ffmpeg_end(void);
 static void end_ffmpeg_impl(int is_autosplit);
 
 #ifdef WITH_AUDASPACE