[clang] [clang] Allow `$` in identifiers during preprocessing (PR #200614)

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

The test failures are related.

I do not buy the "Since it seems highly undesirable to have preprocessing depend on target capabilities" - currently it depends only on `-fdollars in identifiers` and the behavior of that option is consistent with the behavior of the preprocessor.

Therefore I do not see a motivation for this patch beside "I want to use $ in macros"

https://github.com/llvm/llvm-project/pull/200614