[libc++abi] Add an option to avoid demangling in terminate.

We've been using this patch in Android so we can avoid including the
demangler in libc++.so. It comes with a rather large cost in RSS and
isn't commonly needed.

Reviewed By: #libc_abi, compnerd

Differential Revision: https://reviews.llvm.org/D88189

GitOrigin-RevId: 866d480fe0549d616bfdd69986dd07a7b2dc5b52
2 files changed