Work on ANSI C compatibility: modifying the github workflow

Work on ANSI C compatibility: modifying the github workflow

The github workflow that attempts to check that OpenSSL ANSI C compatible
defined '_DEFAULT_SOURCE', which effectively turns gcc and clang into a C99
compiler...  perhaps not with regard to pure language features, but it enables
a few too many types and functions that aren't defined in ANSI C library, or
in some cases, in any C language level library.

Instead of '_DEFAULT_SOURCE', this modification defines '_XOPEN_SOURCE=1' and
'_POSIX_SOURCE=200809L', to enable the use of 'timezone', 'ssize_t' and 'strdup()'.

Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24173)