If we don't build pkg-config (because a previous installation exists
somewhere else), autoconf won't find PKG_* m4 macros and fail to
run on packages using them (if they don't ship the macros either)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit b590a13f930a14040047ac2203ca64afb1c0c38d)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>