[pango] Use $PKG_CONFIG instead of pkg-config consistently

[Behdad Esfahbod <behdad src gnome org>]

commit dd76b439506c650aa48ae160811c5ec4b8b7447d
Author: Behdad Esfahbod <behdad behdad org>
Date:   Sat Mar 26 09:23:38 2016 -0700

    Use $PKG_CONFIG instead of pkg-config consistently
    
    Fixes https://bugzilla.gnome.org/show_bug.cgi?id=764191

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 8af7dfd..34e6e97 100644
--- a/configure.ac
+++ b/configure.ac
@@ -500,7 +500,7 @@ AC_ARG_ENABLE(doc-cross-references,
 
 if test "x$enable_doc_cross_references" != xno ; then
        GLIB_PREFIX="`$PKG_CONFIG --variable=prefix glib-2.0`"
-       CAIRO_PREFIX="`pkg-config --variable=prefix cairo`"
+       CAIRO_PREFIX="`$PKG_CONFIG --variable=prefix cairo`"
        AC_SUBST(GLIB_PREFIX)
        AC_SUBST(CAIRO_PREFIX)
 fi