Fix typos in comments.

Reported by Josh Soref <jsoref@gmail.com> in
<https://lists.gnu.org/r/bug-gnulib/2023-06/msg00057.html>.

* src/sigsegv.h.in: Fix a typo.
* src/stackvma-cygwin.c: Likewise.
* src/stackvma-freebsd.c: Likewise.
* src/stackvma-netbsd.c: Likewise.
* src/stackvma-rofile.c: Likewise.
* tests/test-catch-segv1.c: Likewise.
* tests/test-catch-segv2.c: Likewise.
* tests/test-catch-stackoverflow2.c: Likewise.
* tests/test-segv-dispatcher1.c: Likewise.