Generic importing Xlib+friends via pkg-config, instead of scanning
through a list of directories. This is very helpful for non-standard
installation pathes and crosscompiling, as the generic pkg-config
infrastructure will handle it all.

Also dropping the obsolete bundled Xext headers.

Conflicts:
	vcl/prj/build.lst

Change-Id: I6ee381030ff9f1d2d83062a17ab55ad3d847a4c6