fix TryToFixInvalidVariablyModifiedType to reject negative array sizes

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@63557 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index d03879e..21fe6e1 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -3114,9 +3114,10 @@
     
   assert(EvalResult.Val.isInt() && "Size expressions must be integers!");
   llvm::APSInt &Res = EvalResult.Val.getInt();
-
-  return Context.getConstantArrayType(VLATy->getElementType(),
-                                      Res, ArrayType::Normal, 0);
+  if (Res >= llvm::APSInt(Res.getBitWidth(), Res.isUnsigned()))
+    return Context.getConstantArrayType(VLATy->getElementType(),
+                                        Res, ArrayType::Normal, 0);
+  return QualType();
 }
 
 bool Sema::VerifyBitField(SourceLocation FieldLoc, IdentifierInfo *FieldName,