[clang] [WIP][clang] Fix std::tm etc. mangling on Solaris (PR #106353)

[Rainer Orth via cfe-commits]

rorth wrote:

> > just leads to infinite recursion (obviously),
> 
> Try casting the pointer to uintptr_t?

That just created a total mess, unfortunately, like duplicating args or dropping the `*` from `char const *`.

> Might be simpler to mess with CXXNameMangler::mangleUnscopedName, though, which I think is where the St prefix is getting added.

This worked seamlessly indeed.  Thanks for the suggestion.  I'm currently running a last round of testing and will post the working patch once I'm done.

https://github.com/llvm/llvm-project/pull/106353