Set SA_ONSTACK in zend_sigaction External

Hi, internals! It's been a while. I'm currently working on a new SAPI for web servers written in Go. Many virtual machines, including Go ( https://pkg.go.dev/os/signal#hdr-Go_programs_that_use_cgo_or_SWIG), depend on signals using SA_ONSTACK ( https://man7.org/linux/man-pages/man2/sigaltstack.2.html). This flag allows a thread to define a new alternate signal stack. Many argue that SA_ONSTACK should be a default, but it's not the case (yet). Python merged a patch setting SA_ONSTACK in 2021 (Python 3.10+) for the same reasons (https://bugs.python.org/issue43390 / https://github.com/python/cpython/commit/02ac6f41e5569ec28d625bb005155903f64cc9ee), with no issues. I opened a Pull Request to set this flag by default and tested it successfully with my Go SAPI: https://github.com/php/php-src/pull/9597 As this is technically at the limit between a new feature and a bug fix (having the ability to call Go/C++ VM code from PHP and embed PHP in such programs), should I open an RFC? Also, if merging my patch is considered, which branch should I target? Cheers, -- Kévin Dunglas