pg_test_fsync crashes on systems with POSIX signal handling

On my old HPUX box:

$ ./pg_test_fsync
2 seconds per test
Direct I/O is not supported on this platform.

Compare file sync methods using one 8kB write:
(in wal_sync_method preference order, except fdatasync
is Linux's default)
open_datasync 165.122 ops/sec ( 6056 microsecs/op)
fdatasync Alarm call
$ echo $?
142 -- that's SIGALRM

The reason it's failing is that according to the traditional (not BSD)
definition of signal(2), the signal handler is reset to SIG_DFL when the
signal is delivered. So the second occurrence of SIGALRM doesn't call
the signal handler but just crashes the process.

The quick-and-dirty fix for this is to just copy pqsignal() into
pg_test_fsync, and use that instead of calling signal() directly.
I wonder though if we shouldn't move that function into libpgport.
Thoughts?

regards, tom lane