openssl: BoringSSL / AWS-LC tidy-ups

openssl: BoringSSL / AWS-LC tidy-ups

- schannel: apply BoringSSL workaround to AWS-LC too.
  Affects Schannel + AWS-LC MultiSSL builds. (not tested in CI)
  Ref: 274940d7438af7ef92ce3e11d75620db94675932 #2643 #2634

- curl_ntlm_core: deduplicate macro defines.

- curl_ntlm_core: document version thresholds for an AWS-LC-specific
  workaround.
  It was necessary between v1.2.0 2022-09-01 and v1.30.1 2024-06-21.
  No longer necessary since v1.31.0 2024-07-01:
  https://github.com/aws/aws-lc/commit/ba94617d99c18949711e8e405721ea85a2b38c3f
  Follow-up to 34ef4fab22d93cf7ef1d6c2954a0bad19f323ea9 #10320

- lib758: drop redundant OpenSSL version guards.
  `OPENSSL_VERSION_NUMBER > 3` automatically guards against LibreSSL,
  BoringSSL and AWS-LC.
  Ref: https://github.com/curl/curl/pull/18288/commits/6ddd8f2c0bbfcb0847b1ee7f257fb772fa47310c
  Follow-up to a5f0ab7995bbb6e269feb3a516f804a65c753705 #18288

- dllmain, curl_sha512_256: formatting.

Closes #18387