Don't pass a null pointer to cast<> in its unit tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162310 91177308-0d34-0410-b5e6-96231b3b80d8

unittests/Support/Casting.cpp

@@ -95,8 +95,9 @@ TEST(CastingTest, cast) {
   EXPECT_NE(&F5, null_foo);
   const foo *F6 = cast<foo>(B4);
   EXPECT_NE(F6, null_foo);
-  foo *F7 = cast<foo>(fub());
-  EXPECT_EQ(F7, null_foo);
+  // Can't pass null pointer to cast<>.
+  // foo *F7 = cast<foo>(fub());
+  // EXPECT_EQ(F7, null_foo);
   foo *F8 = B1.baz();
   EXPECT_NE(F8, null_foo);
 }
@@ -121,7 +122,8 @@ TEST(CastingTest, dyn_cast) {
   EXPECT_NE(F2, null_foo);
   const foo *F3 = dyn_cast<foo>(B4);
   EXPECT_NE(F3, null_foo);
-  // foo *F4 = dyn_cast<foo>(fub()); // not permittible
+  // Can't pass null pointer to dyn_cast<>.
+  // foo *F4 = dyn_cast<foo>(fub());
   // EXPECT_EQ(F4, null_foo);
   foo *F5 = B1.daz();
   EXPECT_NE(F5, null_foo);