Fix a minor bug in isNullPointerConstant triggered by the linux 
tgmath.h.

Note that there is another issue with tgmath.h, so mandel.c still 
doesn't work.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@47069 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/AST/Expr.cpp b/AST/Expr.cpp
index c7a2005..f4da0f0 100644
--- a/AST/Expr.cpp
+++ b/AST/Expr.cpp
@@ -995,7 +995,7 @@
   // Strip off a cast to void*, if it exists.
   if (const CastExpr *CE = dyn_cast<CastExpr>(this)) {
     // Check that it is a cast to void*.
-    if (const PointerType *PT = dyn_cast<PointerType>(CE->getType())) {
+    if (const PointerType *PT = CE->getType()->getAsPointerType()) {
       QualType Pointee = PT->getPointeeType();
       if (Pointee.getQualifiers() == 0 && Pointee->isVoidType() && // to void*
           CE->getSubExpr()->getType()->isIntegerType())            // from int.