[clang] [llvm] [clang][DebugInfo] Mark _BitInt's as reconstitutable when emitting -gsimple-template-names (PR #168383)

[Michael Buch via cfe-commits]

Michael137 wrote:

> The changes to simple-template-names.cpp should, in some part of this series, end up in the cross-project-tests version of the test, so we test the full roundtrip.
> 
> Thanks so much for taking an interest in/improving simplified template names!

I adjusted the `simplified-template-names.s` version of the test in https://github.com/llvm/llvm-project/pull/168382 (there's an remaining question about whether we want the unit-test https://github.com/llvm/llvm-project/pull/168382#discussion_r2535522148)

https://github.com/llvm/llvm-project/pull/168383