Checking __STDC_VERSION__ rather than __STRICT_ANSI__
Checking __STDC_VERSION__ rather than __STRICT_ANSI__

`__STRICT_ANSI__` is a gnuish flag macro that indicates if `-ansi`
was given on the command line.  To check the C version, it's better
to check the macro `__STDC_VERSION__`.

Reviewed-by: Hugo Landau <ce9fa1e55a72fc9b85dd06e47ea2c07848fb7d2c@openssl.org>
Reviewed-by: Shane Lontis <452ce16516ceed26291fe7de3f8b53540d83864e@oracle.com>
Reviewed-by: Tomas Mraz <2bc6038c3dfca09b2da23c8b6da8ba884dc2dcc2@openssl.org>
Reviewed-by: Todd Short <0267f0ecbdb3e99cdfd94eb139bf30919fa04d2f@me.com>
(Merged from https://github.com/openssl/openssl/pull/19197)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl