Handle the GNU void* and function pointer arithmetic extensions for constant expressions as well.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@65013 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/const-eval.c b/test/Sema/const-eval.c
index 7307aea..a565041 100644
--- a/test/Sema/const-eval.c
+++ b/test/Sema/const-eval.c
@@ -32,3 +32,5 @@
 
 // ?: in constant expressions.
 int g17[(3?:1) - 2]; 
+
+EVAL_EXPR(18, (int)((void*)10 + 10));