qmlglsink: fix build on EGL platform without X11 headers
If Mesa is built without X11 headers, building against Mesa EGL headers requires a dependency on egl.pc, to define MESA_EGL_NO_X11_HEADERS. This fixes a build error when compiling ext/qt/gstqtglutility.cc:
In file included from /usr/include/EGL/egl.h:39,
from /usr/include/gstreamer-1.0/gst/gl/egl/gstegl.h:44,
from ../gst-plugins-good-1.16.1/ext/qt/gstqtglutility.cc:43:
/usr/include/EGL/eglplatform.h:124:10: fatal error: X11/Xlib.h: No such file or directory
Edited by Matthew Waters