Integrate perlio:

[  8408]
Remove variables that were used in experiments.

[  8407]
Catch die in %SIG handler and unblock the signal before re-dying.
This make Linux work _without_ sigsetjmp().
Turn off sigsetjmp() to see what else it does.
May need Configure probe for sigprocmask() if anything has sigaction()
but not sigprocmask().

p4raw-link: @8408 on //depot/perlio: e86d18fb728c811dd6c2cb46964683c4547de3e7
p4raw-link: @8407 on //depot/perlio: 1b266415f383a85c93346bb15a7bdcac7f62eb77

p4raw-id: //depot/perl@8409