[clang] Disable -fdollars-in-identifiers by default (PR #135407)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> We should disable the warning if we're preprocessing asm, which should mostly solve the issue with warnings.

Effectively checking for `LangOpts.DollarIdents || LangOpts.AsmPreprocessor`? Or do you think `DollarIdents` should be true if `AsmPreprocessor` is true?

https://github.com/llvm/llvm-project/pull/135407