Don't try to build dmx/input/usb-*.c if <linux/input.h> isn't found
Replace -rdynamic with $(LD_EXPORT_SYMBOLS_FLAG) for compatibility with
compilers other than gcc
Fix the dri and drm build. Fix server-side DMX extension build. Make
xf4bpp use the correct version of mfbline.c for mfbseg.c. Add #ifndef
_HEADERNAME_H_/#define _HEADERNAME_H_/.../#endif to the headers.