- fix internal macro `AN_APPLE_OS` reused between sources without
resetting it. It may potentially have left the system sha256
function unused.
- fix to define `WOLFSSL_OPTIONS_IGNORE_SYS` so that it always applies
to wolfSSL headers, also during feature detection.
- md4, md5, sha256: simplify fallback logic.
- delete 20+ unused macros.
- scope or move macros to avoid `-Wunused-macros` warnings.
- examples: delete unused code.
The warning detects macros defined but not used within the same C
source. It does not warn for macros defined in headers. It also works
with unity builds, but to a lesser extent.
Closes#20593
5fa5cb3825