[clang][ASTReader] Fix memory leak while reading FriendTemplateDecls

Allocate on ASTContext, rather than just on heap, so that template
parameter lists are freed up.

Differential Revision: https://reviews.llvm.org/D120081

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -2103,7 +2103,7 @@ void ASTDeclReader::VisitFriendTemplateDecl(FriendTemplateDecl *D) {
   VisitDecl(D);
   unsigned NumParams = Record.readInt();
   D->NumParams = NumParams;
-  D->Params = new TemplateParameterList*[NumParams];
+  D->Params = new (Reader.getContext()) TemplateParameterList *[NumParams];
   for (unsigned i = 0; i != NumParams; ++i)
     D->Params[i] = Record.readTemplateParameterList();
   if (Record.readInt()) // HasFriendDecl