[cairo] MMX_CFLAGS and AC_SUBST

[Baz]

I was just putting together the altivec patches for publishing and I
noticed an oddity in the pixman configure.in.

Commit 0263f18f843175e478bd3a14e24445e31e7b0952
removed MMX_CFLAGS from pixman/src/Makefile.am, and removed the
corresponding AC_SUBST in the top-level configure.in as well,
replacing it with
PIXMAN_CFLAGS="$PIXMAN_CFLAGS $MMX_CFLAGS"
// ... later...
AC_SUBST(PIXMAN_CFLAGS)

However, in pixman/configure.in, AC_SUBST(MMX_CFLAGS) still appears.
Looks like a mistake? (I'm not sure if/when this configure.in is used,
but thats another issue)

Cheers,
Baz