Inline the trivial S_raise_signal function in the perl signal handler.

Inline the trivial S_raise_signal function in the perl signal handler.

This makes the code more readable and avoids the need for excuses
for why the function is (still) named this way.

It also effectively avoids segfaults observed with gcc-3.3 when
the sibling-call optimization is used for invoking S_raise_signal()
just before the signal handler returns.

p4raw-id: //depot/perl@33741