* nimRawSetjmp: support Windows
Using `_setjmp()` directly is required to avoid some rare (but very
annoying) exception-related stack corruption leading to segfaults on
Windows, with Mingw-w64 and SEH.
More details: https://github.com/status-im/nimbus-eth2/issues/3121
Also add "nimBuiltinSetjmp" - mostly for benchmarking.
* fix for Apple's Clang++
