See for details:
http://lists.altlinux.org/pipermail/devel/2009-March/167877.html

diff --git a/giblib/configure.ac b/giblib/configure.ac
index 6807d86..f3a5f20 100644
--- a/giblib/configure.ac
+++ b/giblib/configure.ac
@@ -23,8 +23,8 @@ AC_PATH_GENERIC(imlib2, 1.0.0, [
   AC_MSG_ERROR(Cannot find imlib2: Is imlib2-config in the path?) )
 
 dnl the above doesn't work for some reason :/
-IMLIB_LIBS=`imlib2-config --libs`
-IMLIB_CFLAGS=`imlib2-config --cflags`
+IMLIB_LIBS=`pkg-config imlib2 --libs`
+IMLIB_CFLAGS=`pkg-config imlib2 --cflags`
 AC_SUBST(IMLIB_LIBS)
 AC_SUBST(IMLIB_CFLAGS)