NOIRLAB: changes in unix/os/zfiotx

[olebole]

These are two commits extracted from NOIRLAB:

1. dcba136 fixed 'var might be clobbered by longjmp' warning on linux

   I can't reproduce the warning on Linux; however the right solution here would not be declaring a static CHAR *abuf, but instead having a volatile XCHAR *op Therefore, the original commit is replaced with this one.

   Also, as tty_getraw is set in (possibly asynchronuous) signal handlers, it must be declared as static volatile sig_atomic_t tty_getraw.

2. cd4dc30, bdfd8e7 catch/ignore EBADF when closing fd on background jobs (Mac)

   These commits look overly complicated.

   -       *status = (fclose(kfp->fp) == EOF && kfp->flags&KF_NOSTTY) ? XERR : XOK;
   +        if ((*status = (fclose(kfp->fp) == EOF && kfp->flags&KF_NOSTTY) ?  XERR : XOK) == XERR) {
   +            if (errno == EBADF)
   +                *status = XOK;
   +        }

   Why not just

        *status = (fclose(kfp->fp) == EOF && errno != EBADF && kfp->flags && KF_NOSTTY)? XERR : XOK;

   Also, Just ignoring an error for EBADF seems not thre right solution - why does EBADF appear in background jobs?

Independent of this, there is a use of fcancel(fp), which is similar to what is in zxwhen.c. There, it was replaced in #366 with something more portable; maybe we should re-use it here (moved to osproto.h?).

Pinging @mjfitzpatrick for a potential discussion.