Use the provided SDL2_mixer target

Instead of relying on variables defined in the FindSDL2_mixer module,
create an IMPORTED target. This allows any overriding system
SDL2_mixerConfig to add additional properties needed for the build
to succeed.

This might help with bugs with vcpkg/macOS.

client/CMakeLists.txt

@@ -165,13 +165,12 @@ endif()
 
 if (AUDIO_SDL)
   target_sources(freeciv21-client PRIVATE audio/audio_sdl.cpp)
+  # SDL comes with the -s option on emscripten
   if (NOT EMSCRIPTEN)
-    # SDL comes with the -s option on emscripten
     # See https://github.com/microsoft/vcpkg/blob/2023.12.12/ports/sdl2/usage
     target_link_libraries(freeciv21-client
       PRIVATE $<IF:$<TARGET_EXISTS:SDL2::SDL2>,SDL2::SDL2,SDL2::SDL2-static>)
-    target_link_libraries(freeciv21-client PRIVATE ${SDL2_MIXER_LIBRARIES})
-    target_include_directories(freeciv21-client PRIVATE ${SDL2_MIXER_INCLUDE_DIR})
+    target_link_libraries(freeciv21-client PRIVATE SDL2_mixer::SDL2_mixer)
   endif()
 endif()
 

cmake/FindSDL2_mixer.cmake

@@ -80,6 +80,13 @@ FIND_PACKAGE_HANDLE_STANDARD_ARGS(SDL2_mixer
                                   REQUIRED_VARS SDL2_MIXER_LIBRARIES SDL2_MIXER_INCLUDE_DIRS
                                   VERSION_VAR SDL2_MIXER_VERSION_STRING)
 
+if (SDL2_MIXER_FOUND)
+  add_library(SDL2_mixer::SDL2_mixer UNKNOWN IMPORTED)
+  set_target_properties(SDL2_mixer::SDL2_mixer PROPERTIES
+                        IMPORTED_LOCATION "${SDL2_MIXER_LIBRARIES}"
+                        INTERFACE_INCLUDE_DIRECTORIES "${SDL2_MIXER_INCLUDE_DIR}")
+endif()
+
 # for backward compatiblity
 set(SDLMIXER_LIBRARY ${SDL2_MIXER_LIBRARIES})
 set(SDLMIXER_INCLUDE_DIR ${SDL2_MIXER_INCLUDE_DIRS})

cmake/FreecivDependencies.cmake

@@ -67,16 +67,14 @@ endif()
 # SDL2 for audio
 find_package(SDL2)
 find_package(SDL2_mixer)
-if (SDL2_MIXER_LIBRARIES AND SDL2_FOUND)
+if (SDL2_MIXER_FOUND AND SDL2_FOUND)
   set(AUDIO_SDL TRUE)
 endif()
 if (NOT SDL2_FOUND)
   message(STATUS "SDL2 not found - audio support disabled")
 endif()
-if (NOT SDL2_MIXER_LIBRARIES)
+if (NOT SDL2_MIXER_FOUND)
   message(STATUS "SDL2_mixer not found - audio support disabled")
-  set(SDL2_MIXER_LIBRARIES "")
-  set(SDL2_MIXER_INCLUDE_DIR "")
 endif()
 
 # Lua