Fix mismatched memory allocation and deallocation. (#6923)

In NestedNameSpecifier.cpp, the Append function allocates data using
`new`:


e1bb926f63/tools/clang/lib/AST/NestedNameSpecifier.cpp (L449-L450)

However, if it deallocated using `free`:


e1bb926f63/tools/clang/lib/AST/NestedNameSpecifier.cpp (L514-L516)

This can cause problems. I'm changing the `free` to `delete`.

tools/clang/lib/AST/NestedNameSpecifier.cpp

@@ -512,7 +512,7 @@ operator=(const NestedNameSpecifierLocBuilder &Other) {
   
   // Free our storage, if we have any.
   if (BufferCapacity) {
-    free(Buffer);
+    delete[] Buffer; // HLSL Change: Use overridable operator delete
     BufferCapacity = 0;
   }
   
@@ -647,7 +647,7 @@ void NestedNameSpecifierLocBuilder::MakeTrivial(ASTContext &Context,
 
 void NestedNameSpecifierLocBuilder::Adopt(NestedNameSpecifierLoc Other) {
   if (BufferCapacity)
-    free(Buffer);
+    delete[] Buffer; // HLSL Change: Use overridable operator delete
 
   if (!Other) {
     Representation = nullptr;

tools/clang/test/SemaHLSL/nestednamespecifier.hlsl

@@ -0,0 +1,17 @@
+// RUN: %dxc -T cs_6_0 -E main -HV 2021 -verify %s
+
+// expected-no-diagnostics
+
+template <typename T>
+class C {
+  C cast();
+};
+
+template <class T>
+C<T>
+C<T>::cast() {
+  C result;
+  return result;
+}
+
+[numthreads(64, 1, 1)] void main() {}