[clang] [llvm] Enable fexec-charset option (PR #138895)

[Hubert Tong via cfe-commits]

hubert-reinterpretcast wrote:

> Is that because you don't want to leave the option in "half-working" state?

Exactly.

> I'm not opposed to doing this as the last step, but is this reqally required?

I think this it is better to maintain a discipline of not enabling features in a half-working state if it is unclear that such a state has compelling value to users.

https://github.com/llvm/llvm-project/pull/138895