tests: make it easier to bypass alarm time in debugger

tests: make it easier to bypass alarm time in debugger

While auditing alarm usage, I noticed that test-regex had a nice
idiom that made it easier to disable an alarm under glibc.  Use
it elsewhere, so future copy-and-paste will preserve the idiom.

* tests/test-file-has-acl.c (main): Allow gdb to override alarm.
* tests/test-memmem.c (main): Likewise.
* tests/test-passfd.c (main): Likewise.
* tests/test-ptsname.c (main): Likewise.
* tests/test-ptsname_r.c (main): Likewise.
* tests/test-strcasestr.c (main): Likewise.
* tests/test-strstr.c (main): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>