[gtk+] Work around a pkg-config bug

[Matthias Clasen <matthiasc src gnome org>]

commit 57751fa391fce8b9f208c41260e8968dd4cdc800
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Oct 18 12:40:18 2014 -0400

    Work around a pkg-config bug
    
    It doesn't report -I${prefix}/include in cflags, even if .pc
    files explicitly put it there. This was breaking the build
    outside of a jhbuild shell when libepoxy is in the jhbuild tree
    but not in /usr.

 configure.ac |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 62c301f..3ca8942 100644
--- a/configure.ac
+++ b/configure.ac
@@ -350,7 +350,8 @@ backend_immodules=
 have_gio_unix=no
 GDK_BACKENDS=
 GDK_EXTRA_LIBS=
-GDK_EXTRA_CFLAGS=
+# expoxy.pc has Cflags: -I${includedir}, but pkg-config swallows that :-(
+GDK_EXTRA_CFLAGS="-I${prefix}/include"
 GDK_WINDOWING=
 PANGO_PACKAGES="pango pangocairo"