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.
- SDL_JoystickGUID -> SDL_GUID (though we retain a type alias)
- Operations for GUID <-> String ops are now in
src/SDL_guid.c and include/SDL_guid.h
- The corresponding Joystick operations delegate to SDL_guid.c
- Added test/testguid.c
- use 'OPTIONS RESOURCE' linker directive, instead of playing tricks on
the built dll.
- build libm sources as a static library and link the dll to with, like
the os/2 makefile does.
- remove *.res with make clean.
