Some uses of non-threadsafe `strerror` have snuck into the code since
they were removed in #4152. Add a wrapper `SysErrorString` for
thread-safe strerror alternatives and replace all uses of `strerror`
with this.
Add `strerror` to the locale-dependence linter to catch its use.
Add an exemption for strerror.cpp (the only allowed use).
Also fix a bug in the regexp so that `_r` and `_s` variants are detected
again.
This is a partial backport of core#24933
https://github.com/bitcoin/bitcoin/pull/24933/commits/46971c6dbfbc39ebbc74ab1ed8c00edc12859373
https://github.com/bitcoin/bitcoin/pull/24933/commits/e3a06a3c6cbb288ac89a2725cf71ae8adaebf35c
Depends on D16208