Fix compilation with MinGW32

[ccawley2011]

There is still one compilation failure remaining in the playground application, which occurs when building with Direct3D or SDL2 (but not GLFW):

d:/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../../mingw32/bin/ld.exe: d:/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../libmingw32.a(main.o):(.text.startup+0xc0): undefined reference to `WinMain@16'
collect2.exe: error: ld returned 1 exit status

The same issue can be observed with MinGW-w64 as well:

D:/msys64/mingw32/bin/../lib/gcc/i686-w64-mingw32/10.3.0/../../../../i686-w64-mingw32/bin/ld.exe: D:/msys64/mingw32/bin/../lib/gcc/i686-w64-mingw32/10.3.0/../../../../i686-w64-mingw32/lib/../lib/libmingw32.a(lib32_libmingw32_a-crt0_c.o): in function `main':
C:/_/M/mingw-w64-crt-git/src/mingw-w64/mingw-w64-crt/crt/crt0_c.c:18: undefined reference to `WinMain@16'

[madebr]

I'm looking into #76 with cmake.
It looks like Android also needs SDL_MAIN_HANDLED defined for dumprwtree (not useful on Android because it is a cli tool, but good to know) and other targets.
I propose to do the following cmake change instead.
Instead of

librw/src/CMakeLists.txt

Line 160 in b2ceadc

target_compile_definitions(librw PUBLIC LIBRW_SDL2)

,
do:

        target_compile_definitions(librw
            PUBLIC
                LIBRW_SDL2
                SDL_MAIN_HANDLED
        )

I guess something similar can be done in the premake script.

We should probably add a call to SDL_SetMainReady at the appropriate places.
See https://wiki.libsdl.org/SDL_SetMainReady

[ccawley2011]

The SDL_MAIN_HANDLED changes have been separated into PR #83.

[madebr]

Can you please update this PR's title + description?
This pr is not doing anything mingw related anymore.
#87 adds mingw support (albeit not to the premake script)

[ccawley2011]

Can you please update this PR's title + description?
This pr is not doing anything mingw related anymore.
#87 adds mingw support (albeit not to the premake script)

This PR is still necessary for the original MinGW (https://osdn.net/projects/mingw/).

[madebr]

Indeed.
And with #87, no more WinMain linking errors.