stlib: Extract SDL_memcpy and SDL_memset to its own file respectively

This is done such that we can disable LTO for these 2 functions when
building with MSVC.

This is due to a limitation of Link Time Code Generation (LTCG).
Code generation might generate a new reference to memset after linking
has started. The LTCG must make assumptions about where memset is
defined which is normally the C runtime.

CMakeLists.txt

@@ -649,6 +649,11 @@ if(MSVC)
   target_compile_definitions(sdl-build-options INTERFACE "-D_CRT_SECURE_NO_WARNINGS")
 endif()
 
+if(MSVC)
+  # Due to a limitation of Microsoft's LTO implementation, LTO must be disabled for memcpy and memset.
+  set_property(SOURCE src/stdlib/SDL_memcpy.c src/stdlib/SDL_memset.c APPEND PROPERTY COMPILE_FLAGS /GL-)
+endif()
+
 if(SDL_ASSEMBLY)
   if(USE_GCC OR USE_CLANG)
     # TODO: Those all seem to be quite GCC specific - needs to be