gmp - need to force GCC 4.2 on 10.6 as well

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

Formula/gmp.rb

@@ -15,7 +15,8 @@ class Gmp <Formula
   def install
     # Reports of problems using gcc 4.0 on Leopard
     # https://github.com/mxcl/homebrew/issues/issue/2302
-    ENV.gcc_4_2 if MACOS_VERSION < 10.6
+    # Also force use of 4.2 on 10.6 in case a user has changed the default
+    ENV.gcc_4_2
 
     fails_with_llvm "Tests fail to compile; missing references in 'llvm bitcode in libtests.a(misc.o)'."