fix FTBS on XSERVER_LIBPCIACCESS
Not all Xserver versions define that symbol with a numeric value (1 or 0), some just might not define it at all when disabled.
Using #if instead of #ifdef (as most sites do) will lead to compile break:
../../src/vmware.c:1102:25: error: expected value in expression
#if XSERVER_LIBPCIACCESS
^
Signed-off-by: Enrico Weigelt, metux IT consult info@metux.net