[cmake] fix ffmpeg libdrm on macos (#367)

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: #367
Reviewed-by: Shinmegumi <shinmegumi@eden-emu.dev>
Reviewed-by: Lizzie <lizzie@eden-emu.dev>

externals/ffmpeg/CMakeLists.txt

@@ -63,6 +63,7 @@ if (NOT WIN32 AND NOT ANDROID)
     set(FFmpeg_HWACCEL_INCLUDE_DIRS)
     set(FFmpeg_HWACCEL_LDFLAGS)
 
+    if (NOT APPLE)
         # In Solaris needs explicit linking for ffmpeg which links to /lib/amd64/libX11.so
         if(PLATFORM_SUN)
             list(APPEND FFmpeg_HWACCEL_LIBRARIES
@@ -77,6 +78,7 @@ if (NOT WIN32 AND NOT ANDROID)
         endif()
         list(APPEND FFmpeg_HWACCEL_FLAGS
             --enable-libdrm)
+    endif()
 
     if(LIBVA_FOUND)
         find_package(X11 REQUIRED)