Predefine __LITTLE_ENDIAN__

It's a nice consistency with some other targets to predefine
__LITTLE_ENDIAN__ for little-endian NaCl targets.  We'd like
to be able to use this in upstream-friendly newlib headers.

BUG= none
TEST= manually examined -dM output

R=pdox@google.com

Review URL: https://chromiumcodereview.appspot.com/9447064
diff --git a/gcc/config/i386/nacl.h b/gcc/config/i386/nacl.h
index e903e02..c82ec28 100644
--- a/gcc/config/i386/nacl.h
+++ b/gcc/config/i386/nacl.h
@@ -196,6 +196,7 @@
     {							\
 	LINUX_TARGET_OS_CPP_BUILTINS();			\
 	builtin_define ("__native_client__=1");		\
+	builtin_define ("__LITTLE_ENDIAN__");		\
   }							\
   while (0)