(interrupt_handler):

(interrupt_handler):
Don't use SA_INTERRUPT to decide whether to call sigaction, as
POSIX.1 doesn't require SA_INTERRUPT and some systems
(e.g. Solaris 7) don't define it.  Use SA_NOCLDSTOP instead;
it's been part of POSIX.1 since day 1 (in 1988).
(install_handler): Use SA_NOCLDSTOP, not _POSIX_VERSION,
to decide whether to call sigaction; this fixes an old typo.