fix linking OpenAL statically on Win32/MXE

Add the necessary AL_LIBTYPE_STATIC define for MXE and non-msys2 win32
builds so that OpenAL can be linked statically without errors.

src/wx/CMakeLists.txt

@@ -45,6 +45,10 @@ endif(NOT ENABLE_DIRECT3D)
 if(ENABLE_OPENAL)
     FIND_PACKAGE(OpenAL REQUIRED)
     INCLUDE_DIRECTORIES(${OPENAL_INCLUDE_DIR})
+
+    IF(WIN32 AND ((NOT (MINGW AND MSYS)) OR CMAKE_TOOLCHAIN_FILE MATCHES mxe))
+        ADD_DEFINITIONS(-DAL_LIBTYPE_STATIC)
+    ENDIF()
 else(ENABLE_OPENAL)
     ADD_DEFINITIONS (-DNO_OAL)
 endif(ENABLE_OPENAL)