[PATCH 3/3] platform: fix missing sigisemptyset

[Daniel Borca]

True.  Ironically, one occurence of sigisemptyset (out of two) is in
hush.c and tries to shortcircuit exactly that kind of iteration, at the
start of the loop in check_and_run_traps().  Basically, that one can be
ifdef'ed out if HAVE_SIGISEMPTYSET is undefined.

Rich Felker wrote:
>
> This is not a suitable fallback implementation. It's not needed on
> musl (we provide sigisemptyset), but if this version were used, it
> would give the wrong results, because musl's sigemptyset only fills
> the first _NSIG-1 bits and ignores the remaining ~900 bits of junk in
> sigset_t.
>
> A valid fallback for sigisemptyset would be something like:
>
> 	int empty = 1, i;
> 	for (i=1; i<_NSIG; i++) {
> 		if (sigismember(set, i)>0) {
> 			empty = 0;
> 			break;
> 		}
> 	}
>
> If _NSIG is unknown (not defined), sizeof(sigset_t)*8+1 could work in
> its place, assuming signals are numbered sequentially.

-dborca