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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Closing this PR as it goes in the opposite direction to where WG21 is heading with https://wg21.link/P4234 which SG16 recommends should allow dollars in identifiers unconditionally. If the committee changes directions again, we can always reopen this.

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