[Sema] Revert the change in r200622 that allowed integer casts to silence -Wnon-literal-null-conversion in C code.

It is actually useful to warn in such cases, thanks to Dmitri for pushing on this and making us see the light!

Related to rdar://15925483 and rdar://15922612. The latter radar is where the usefulness of the warning is most clear.

llvm-svn: 201165
diff --git a/clang/test/Sema/warn-null.c b/clang/test/Sema/warn-null.c
index 28ec631..3bf2aed 100644
--- a/clang/test/Sema/warn-null.c
+++ b/clang/test/Sema/warn-null.c
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 %s -verify
 
-#define NLL (unsigned long long)0
+#define SOME_ADDR (unsigned long long)0
 
 // PR10837: Warn if a non-pointer-typed expression is folded to a null pointer
 int *p = 0;
@@ -10,5 +10,5 @@
   p = 0;
   q = '\0'; // expected-warning{{expression which evaluates to zero treated as a null pointer constant}}
   r = 1 - 1; // expected-warning{{expression which evaluates to zero treated as a null pointer constant}}
-  p = NLL;
+  p = SOME_ADDR; // expected-warning{{expression which evaluates to zero treated as a null pointer constant}}
 }