Set USE_SYSTEM_OPENAL default to OFF on macOS and Windows

On Linux, using system libraries is generally preferred, but this is
less relevant on macOS and Windows. In particular, macOS does not
provide "alext.h" in its OpenAL framework, which causes the build to
fail.

Author: pastalian

CMakeLists.txt

@@ -15,6 +15,12 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
     endif()
 endif()
 
+if(APPLE OR WIN32)
+    set(USE_SYSTEM_OPENAL_DEFAULT OFF)
+else()
+    set(USE_SYSTEM_OPENAL_DEFAULT ON)
+endif()
+
 option(USE_NATIVE_INSTRUCTIONS "USE_NATIVE_INSTRUCTIONS makes rpcs3 compile with -march=native, which is useful for local builds, but not good for packages." ON)
 option(WITH_LLVM "Enable usage of LLVM library" ON)
 option(BUILD_LLVM "Build LLVM from git submodule" OFF)
@@ -28,7 +34,7 @@ option(USE_PRECOMPILED_HEADERS "Use precompiled headers" OFF)
 option(USE_SDL "Enables SDL input handler" OFF)
 option(USE_SYSTEM_SDL "Prefer system SDL instead of the builtin one" ON)
 option(USE_SYSTEM_FFMPEG "Prefer system ffmpeg instead of the prebuild one" OFF)
-option(USE_SYSTEM_OPENAL "Prefer system OpenAL instead of the prebuild one" ON)
+option(USE_SYSTEM_OPENAL "Prefer system OpenAL instead of the prebuild one" ${USE_SYSTEM_OPENAL_DEFAULT})
 option(USE_SYSTEM_CURL "Prefer system Curl instead of the prebuild one" ON)
 option(USE_SYSTEM_OPENCV "Prefer system OpenCV instead of the builtin one" ON)
 option(HAS_MEMORY_BREAKPOINTS "Add support for memory breakpoints to the interpreter" OFF)