sdl2: Use SDL2's CMake-based build system

[mborgerson]

This patch migrates SDL2 from the autotools build system to the CMake build system. This appears to be the preferred route now, as both libsdl project CI and MSYS2 both use the CMake path. Three patches are added to fixup minor build issues, two of which originate from the MSYS2 project.

[lephilousophe]

@tonytheodore @mabrand I don't know what happened, but it seems the commit in this PR got its way in the build-2022-04-09 tag while this PR is not merged.
I wonder which action was intended, but it's now in a kind of quantum state.

[lephilousophe]

In addition, this PR breaks SDL2 build in the tag because the patches are outdated

[tonytheodore]

I must have created that tag from a testing branch that included this PR, but the patches fail as you mentioned.

Are there any downsides to deleting the tag?

[lephilousophe]

I don't know, maybe some people using this tag will find it vanished?
A unclean way would be to recreate it with the same name but without this commit. Maybe it's the safest?

[tonytheodore]

Are there any downsides to deleting the tag?

https://git-scm.com/docs/git-tag#_on_re_tagging

I'll leave it as-is and go back to annotated tags that have some notes about how complete the build is:

• https://github.com/mxe/mxe/releases/tag/build-2021-04-22
• https://github.com/mxe/mxe/releases/tag/build-2021-01-10

There are many broken packages and this tag would have been:

echo "MXE_USE_CCACHE := no" >> settings.mk && \
echo "EXCLUDE_PKGS = ocaml%" >> settings.mk && \
[...]
MXE_BUILD_PKG_TARGETS="`echo {i686-w64-mingw32,x86_64-w64-mingw32}.{static,shared}.gcc11`" \
MXE_BUILD_PKG_PKGS='qt5 qt6 gtkmm3 wxwidgets'

[tonytheodore]

@mborgerson, can you rebase this PR against the updated SDL2 versions from #2801

[mborgerson]

@mborgerson, can you rebase this PR against the updated SDL2 versions from #2801

A bit surprised to see activity on this now. Thanks for reviewing.

I've pushed an updated patch to resolve the conflicts from #2801 being merged first, and updated the patches to work with this release of SDL.

The test case builds and this works for my application, but I have not done further testing on it.

By the way, 2.0.22 is coming soon and this patch works for it but will need a minor update, so I can PR an update when it finally releases. out. Patch updated.

[mborgerson]

Rebased and updated to 2.26.2, bumping for review. cc @tonytheodore