bash fails to compile on systems with select() but not pselect()

[Larkin Nickle]

On systems with select() but without pselect(), bash fails to compile 
due to what is possibly a bug in `lib/sh/input_avail.c`. This was tested 
on Tru64 with the bash 5.1 source being built with GCC 4.7.4 on an 
AlphaServer 1000A.

gcc -c   -I. -I../.. -I../.. -I../../lib -I../../include -I. 
-DHAVE_CONFIG_H -DSHELL  -g -O2 -Wno-parentheses -Wno-format-security 
input_avail.c
input_avail.c: In function 'nchars_avail':
input_avail.c:131:46: error: 'set' undeclared (first use in this function)
input_avail.c:131:46: note: each undeclared identifier is reported only 
once for each function it appears in
input_avail.c:135:17: error: 'oset' undeclared (first use in this function)
Around line 110:

#if defined(HAVE_SELECT)
  fd_set readfds, exceptfds;
#endif
#if defined (HAVE_PSELECT)
  sigset_t set, oset;
#endif

Notice that `set` is only defined if HAVE_PSELECT is defined.

Later, around line 130:

#if defined (HAVE_SELECT) || defined (HAVE_PSELECT)
  sigprocmask (SIG_BLOCK, (sigset_t *)NULL, &set);
#  ifdef SIGCHLD
  sigaddset (&set, SIGCHLD);
#  endif
  sigemptyset (&oset);
#endif

You can see that `sigprocmask (SIG_BLOCK, (sigset_t *)NULL, &set);` will 
be reached even if HAVE_PSELECT isn't defined due to HAVE_SELECT being 
defined, which is an issue on systems without a pselect() implementation 
as `set` is never declared.

I believe that this isn't an issue on other platforms that have no 
pselect() out of the box as gnulib has pselect() implementations for 
them, which is not the case on Tru64.

Larkin