basic SDL2 on cosmo

x11/xcb libaries can be built with
CC=x86_64-unknown-cosmo-cc PKG_CONFIG_PATH=$PWD/../output/share/pkgconfig:$PWD/../output/lib/pkgconfig ./autogen.sh --prefix=$PWD/../output --disable-shared --enable-static
make
make install

sdl2 can be built with
./autogen.sh
CC=x86_64-unknown-cosmo-cc PKG_CONFIG_PATH=$PWD/../output/share/pkgconfig:$PWD/../output/lib/pkgconfig ./configure --prefix=$PWD/../output --disable-shared --enable-static --disable-diskaudio --disable-pulseaudio --disable-sndio --disable-video-kmsdrm --disable-video-opengles2 --disable-video-wayland --disable-video-vulkan --enable-video-x11 --disable-dbus --disable-ime --disable-fcitx --disable-joystick-virtual --disable-cpuinfo --disable-joystick --disable-haptic --disable-hidapi --disable-sensor --disable-power --disable-locale --disable-loadso --x-includes=/home/joshua/src/src/cosmo/gui/xlib/output/include --x-libraries=/home/joshua/src/src/cosmo/gui/xlib/output/lib
make
make install

I tried cosmocc instead of x86_64-unknown-cosmo-cc but it failed because aarch64 versions of libaries were not made as so exec building failed.

Working build order:
xorgproto from https://gitlab.freedesktop.org/xorg/proto/xorgproto
xcbproto from https://gitlab.freedesktop.org/xorg/proto/xcbproto
libxau from https://gitlab.freedesktop.org/xorg/lib/libxau
libxcb from https://gitlab.freedesktop.org/xorg/lib/libxcb
libxtrans from https://gitlab.freedesktop.org/xorg/lib/libxtrans
libx11 from https://gitlab.freedesktop.org/xorg/lib/libx11
  add the following in src/XlibInt.c, same as https://github.com/jart/cosmopolitan/issues/1139, required for struct pollfd
    #ifdef __COSMOPOLITAN__
    #include "libc/sock/struct/pollfd.h"
    #endif
libxext from https://gitlab.freedesktop.org/xorg/lib/libxext
sdl2 from https://github.com/libsdl-org/SDL
  tested with release-2.30.3
  comment/remove the sys/sysctl.h include in src/cpuinfo/SDL-cpuinfo.c, header does not exist, sys/types.h has macos only sysctlbyname
  add the following in src/thread/pthread/SDL_systhread.c, required for SCHED constants
    #ifdef __COSMOPOLITAN__
    #include <time.h>
    #endif

With https://en.wikibooks.org/wiki/X_Window_Programming/Xlib's demo as x11demo.c
x86_64-unknown-cosmo-cc -o x11test x11test.c -I output/include -L output/lib -lX11 -lxcb -lXau
apelink -o x11test.com -l /opt/cosmo/.cosmocc/3.3.5/bin/ape-x86_64.elf x11test

With https://github.com/xyproto/sdl2-examples/blob/main/c18/main.c as sdltest.c and grumpy-cat.bmp downloaded, update the path in sdltest.c as required.
x86_64-unknown-cosmo-cc -o sdltest sdltest.c -I output/include -L output/lib -l SDL2 -l X11 -l xcb -l Xau -l Xext
apelink -o sdltest.com -l /opt/cosmo/.cosmocc/3.3.5/bin/ape-x86_64.elf sdltest

Only tested on linux but with minimal tweaking other unix likes should work without much issue.
Windows may be a massive pain and it may end up being easier to use a shared libary for sdl so that it can be swapped out for one supporting windows(gdi specifically?).