Consolidate all the X11 libraries, so you don't have to update 12 different places in the source when adding a new one. Also handles build systems that don't define a given library.

Makefile.in
Makefile
.libs
*.o
*.lo
*.la
SDL_systhread.c
SDL_systhread_c.h
SDL_syssem.c
SDL_syssem_c.h
SDL_sysmutex.c
SDL_sysmutex_c.h
SDL_syscond.c
SDL_syscond_c.h
clone.S