PostgreSQL: build uuid-ossp with _XOPEN_SOURCE.

Fixes build on Mountain Lion

Fixes Homebrew#10315.
Fixes Homebrew#13639.
Closes Homebrew#13803.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Library/Formula/postgresql.rb

@@ -21,8 +21,9 @@ def options
 
   skip_clean :all
 
+  # Fix PL/Python build: https://github.com/mxcl/homebrew/issues/11162
+  # Fix uuid-ossp build issues: http://archives.postgresql.org/pgsql-general/2012-07/msg00654.php
   def patches
-    # Fix PL/Python build: https://github.com/mxcl/homebrew/issues/11162
     DATA
   end
 
@@ -218,3 +219,14 @@ def startup_plist
  endif
 
  # If we don't have a shared library and the platform doesn't allow it
+--- a/contrib/uuid-ossp/uuid-ossp.c	2012-07-30 18:34:53.000000000 -0700
++++ b/contrib/uuid-ossp/uuid-ossp.c	2012-07-30 18:35:03.000000000 -0700
+@@ -9,6 +9,8 @@
+  *-------------------------------------------------------------------------
+  */
+
++#define _XOPEN_SOURCE
++
+ #include "postgres.h"
+ #include "fmgr.h"
+ #include "utils/builtins.h"