x11-links rejects xf86vidmodeproto because it's too old according
to the pkgsrc X xf86vidmodeproto bl3 file (which is at best dubious
logic) and doesn't link it. Then the .pc file isn't available, so
this package's configure script silently fails running pkg-config
and sets XVIDTUNE_LIBS to empty. The build then fails at link time
because no X libs at all have been requested. Fix it by feeding in
the result of running the same pkg-config invocation outside
pkgsrc. The fact that the native xf86vidmode is "too old" does not
itself break the package.
