[gegl] Prefer clang as the compiler on OSX >= 10.7

[Daniel Sabo <daniels src gnome org>]

commit becdbd5d70b9b8a51d60954d79b5c67a4294e9f4
Author: Daniel Sabo <DanielSabo gmail com>
Date:   Thu Oct 10 05:18:19 2013 -0700

    Prefer clang as the compiler on OSX >= 10.7

 configure.ac |   26 +++++++++++++++++++++++++-
 1 files changed, 25 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index bfc3115..f567090 100644
--- a/configure.ac
+++ b/configure.ac
@@ -132,16 +132,40 @@ AC_SUBST(LUA_REQUIRED_VERSION)
 
 dnl ==========================================================================
 
+AC_CANONICAL_SYSTEM
 AM_INIT_AUTOMAKE([1.11 no-define dist-bzip2 no-dist-gzip -Wno-portability])
 dnl Initialize maintainer mode
 AM_MAINTAINER_MODE([enable])
 
-
 ###############
 # Generic stuff
 ###############
 
+dnl Prefer clang on OSX, because GCC isn't updated
+
+case "$build_os" in
+  darwin10.* | darwin9.* | darwin8.*)
+    ;;
+  darwin*)
+    prefered_cc="clang"
+    prefered_cxx="clang++"
+    ;;
+  *)
+    ;;
+esac
+
+if test -z "$CC" && test -n "$prefered_cc"; then
+  AC_MSG_NOTICE([setting CC to $prefered_cc for $build_os])
+  CC=$prefered_cc
+fi
+
+if test -z "$CXX" && test -n "$prefered_cc"; then
+  AC_MSG_NOTICE([setting CXX to $prefered_cxx for $build_os])
+  CXX=$prefered_cxx
+fi
+
 dnl Checks for programs.
+
 AC_PROG_CC
 AC_PROG_CC_C99
 AC_PROG_CXX