Use sigset_t and sigfillset instead of memset

Use sigset_t and sigfillset instead of memset

Rather than using an arbitrary array memset to ones as our signal
mask, use the POSIX sigfillset function and eliminate the static
variable.  Fixes strict aliasing errors with --enable-checking and
gcc 4.4.3 on Linux x86.

Change-Id: Ic3e0499d03657d94f60808ed12e090dc62cce6fc
Reviewed-on: http://gerrit.openafs.org/1616
Tested-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>