Add cflags and libs for X11

fbxkb 1.0 would not be compiled without this patch and fails with message

/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.4/../../../../x86_64-pc-linux-gnu/bin/ld: fbxkb.o: undefined reference to symbol 'XSetErrorHandler'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.4/../../../../x86_64-pc-linux-gnu/bin/ld: note: 'XSetErrorHandler' is defined in DSO /usr/lib64/libX11.so.6 so try adding it to the linker command line
/usr/lib64/libX11.so.6: could not read symbols: Invalid operation