[clang] [include-cleaner] Support multi-header symbols in mapping generator (PR #147720)

[kadir çetinkaya via cfe-commits]

https://github.com/kadircet commented:

thanks, looks a lot better. some small comments around adding a variant for `std::abs` and deleting special entries for global atomic_*

https://github.com/llvm/llvm-project/pull/147720