pkgconfig: Add our bindir to xkbcomp.pc

Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>

xkbcomp.pc.in

 prefix=@prefix@
+bindir=@bindir@
 datarootdir=@datarootdir@
 datadir=@datadir@
 xkbconfigdir=@XKBCONFIGROOT@