[Libva] DSO regression issue

[Xiang, Haihao]

Hi, Gwenole

Your recent commits in libva staging branch result in DSO regression
issue.

make[3]: Entering directory `/home/cc/libva/test/encode'
  CCLD   h264encode
/usr/bin/ld: h264encode_x11.o: undefined reference to symbol 'XOpenDisplay'
/usr/bin/ld: note: 'XOpenDisplay' is defined in DSO /opt/X11R7/lib/libX11.so.6 so try adding it to the linker command line
/opt/X11R7/lib/libX11.so.6: could not read symbols: Invalid operation
collect2: ld returned 1 exit status
make[3]: *** [h264encode] Error 1

Could you take a look and fix it ?

Thanks
Haihao