[clang] [clang][Tooling] Reuse standard-library symbol descriptors (PR #202663)

[Alexis Engelke via cfe-commits]

aengelke wrote:

I usually don't work on Clang and I'm not at all familiar with this part. I'd suggest finding reviewers who worked on this code before.

(What strikes me odd, though, is that the include files are already generated. Maybe the script should generate better output? But I haven't really got a clue where this is used etc., so I'm the wrong person to make judgement calls here.)

https://github.com/llvm/llvm-project/pull/202663