jhbuild: Group external modules at top of moduleset
jhbuild: Group external modules at top of moduleset

A few of the non-X.Org modules such as pixman and libdrm were mixed in
with the X.Org libraries. Instead, they should be at the top of the
moduleset with the rest of the external modules such as fontconfig.

This also adds comments to mark each section separately.

Signed-off-by: Dan Nicholson <2570c412b7cbb4203ff39baaca2bd49e72848226@gmail.com>
Reviewed-by: Dirk Wallenstein <0094b88488405ee50298c1549891ed49bcd7831f@t-online.de>

freedesktop-unofficial-mirror/xorg__util__modular,freedesktop-unofficial-mirror/xorg__util__modular,freedesktop-unofficial-mirror/xorg__util__modular