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.

llvm-svn: 47069

clang/AST/Expr.cpp

@@ -995,7 +995,7 @@ bool Expr::isNullPointerConstant(ASTContext &Ctx) const {
   // 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.

clang/test/Sema/conditional-expr.c

@@ -31,5 +31,8 @@ void foo() {
   enum {xxx,yyy,zzz} e, *ee;
   short x;
   ee = ee ? &x : ee ? &i : &e; // expected-warning {{pointer type mismatch}}
+
+  typedef void *asdf;
+  *(0 ? (asdf) 0 : &x) = 10;
 }