Use signal(sig, SIG_DFL); raise(sig); instead of abort() (#6518)

Use signal(sig, SIG_DFL); raise(sig); instead of abort() (#6518)

As discussed in #6484 (and https://www.gnu.org/software/libc/manual/html_node/Termination-in-Handler.html), simply calling std::abort at the end of a custom signal handler seems to be bad practice. As suggested, this PR changes these calls to instead first reset to the default signal handler for the given signal, and then calling it.
Fixes #6484.