regexec.c, locale.c: Silence some compiler warnings

For regexec.c, one compiler amongst our smokers believes there is a path
where this array can be used uninitialized; it's easiest to just
initialize it, even though I think the compiler is wrong, unless it is
optimizing incorrectly, in which case, it would be still be best to
initialize it.

For locale.c, this is just the well-known gcc bug that they refuse to
fix concerning a (void) cast when the function has been declared to
require not ignoring the resul
regcomp.h: Rmv false comments

I misread the code when I added these comments
pod/perldebguts: Stress ephemeral nature of regnode types