_longjmp
========

POSIX specification:
 https://pubs.opengroup.org/onlinepubs/9699919799/functions/_longjmp.html

Gnulib module: ---

Portability problems fixed by Gnulib:

Portability problems not fixed by Gnulib:

  * This function is missing on some platforms: mingw, MSVC 14.

  * POSIX says this function is obsolescent and it is planned to be removed in POSIX 202x.

Note: Despite its being removed from POSIX, in 2023 on all systems which have _setjmp, it is the fastest way to save the registers but not the signal mask (up to 30 times faster than setjmp on some systems).