Use clang on Mac OS X, which is required for the @autorelease keyword

configure.in

@@ -32,6 +32,16 @@ AC_SUBST(SDL_INTERFACE_AGE)
 AC_SUBST(SDL_BINARY_AGE)
 AC_SUBST(SDL_VERSION)
 
+dnl On Mac OS X we need to build with clang
+dnl We can't use $host or reorder AC_CANONICAL_HOST because of autoconf magic.
+case "`/bin/sh $ac_aux_dir/config.guess`" in
+    *-*-darwin*)
+        if test "x$CC" = "x"; then
+            CC=clang
+        fi
+        ;;
+esac
+
 # libtool versioning
 LT_INIT([win32-dll])