src: don't reset embeder signal handlers
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact.
Fix #47013 (closed)