build fails if libx264-dev is not installed on the host
after commit 0f55b18c building fails if an older libx264 library is installed on the host system. I made sure I updated gst-plugins-ugly.
It's the x264 subproject itself which fails, trying to link aginst the older system version instead of itself.
This can be reproduced on Debian by installing
libx264-dev (version 0.155.2917+git0a84d98).
Removing the system dependency works around the problem.