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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

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

For the Linux kernel, does anything break other than the warnings?

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