cmake: allow overriding GME_ZLIB and GME_UNRAR options by user

(cherry picked from commit 62a4100)

Author: mechakotik

CMakeLists.txt

@@ -591,8 +591,7 @@ if(SDL2MIXER_GME)
         set(BUILD_SHARED_LIBS "${SDL2MIXER_GME_SHARED}")
         set(ENABLE_UBSAN OFF)
         set(BUILD_FRAMEWORK OFF)
-        set(GME_ZLIB OFF)
-        set(GME_UNRAR OFF)
+        option(GME_ZLIB "Enable GME to support compressed sound formats" OFF)
         message(STATUS "Using vendored libgme")
         sdl_check_project_in_subfolder(external/libgme libgme SDL2MIXER_VENDORED)
         add_subdirectory(external/libgme EXCLUDE_FROM_ALL)