xkbcomp.h: include config.h before any other headers
Ensures flags set by AC_USE_SYSTEM_EXTENSIONS are correctly propogated when including system headers.
Closes: #22 (closed) xkbcomp from git compile error
Fixes: 81e46cab ("Use asprintf() if the platform supports it")
Signed-off-by: Alan Coopersmith alan.coopersmith@oracle.com