Use strtol instead of std::stoi [PR110646]

Implementation of std::stoi was overlooked on hppa-hpux, so use
strtol instead.

2023-08-11  John David Anglin  <danglin@gcc.gnu.org>

gcc/ChangeLog:

	PR bootstrap/110646
	* gensupport.cc(class conlist): Use strtol instead of std::stoi.