fix: enable -Wcast-qual flag for libcrypto=awslc

[boquan-fang]

Resolved issues:

resolves #4710

Description of changes:

• Remove the condition which only add -Wcast-qual back for non AWS-lc Libcrypto.

Call-outs:

Testing:

• Local testing without specifying S2N_LIBCRYPTO=openssl.
• CI should test it as well with AWSLC and AWSLC-FIPS.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

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[boquan-fang]

This PR should be unblocked. The original problem is caused by AWSLC having cast-qual issue, and it is fixed now.

This was the original problem with compilation:

/codebuild/output/src2687327939/src/github.com/aws/s2n-tls/crypto/s2n_kyber_evp.c: In function 's2n_kyber_evp_decapsulate':
/codebuild/output/src2687327939/src/github.com/aws/s2n-tls/crypto/s2n_kyber_evp.c:83:30: error: cast discards 'const' qualifier from pointer target type [-Werror=cast-qual]
   83 |                              (uint8_t *) ciphertext, kem->ciphertext_length),
      |                              ^
/codebuild/output/src2687327939/src/github.com/aws/s2n-tls/utils/s2n_ensure.h:35:15: note: in definition of macro '__S2N_ENSURE'
   35 |         if (!(cond)) {             \
      |               ^~~~
/codebuild/output/src2687327939/src/github.com/aws/s2n-tls/crypto/s2n_kyber_evp.c:82:5: note: in expansion of macro 'POSIX_GUARD_OSSL'
   82 |     POSIX_GUARD_OSSL(EVP_PKEY_decapsulate(kyber_pkey_ctx, shared_secret, &shared_secret_size,
      |     ^~~~~~~~~~~~~~~~

We have removed that s2n_kyber_evp.c, and compilation with AWSLC and AWSLC-FIPS are succeeding. We should generalize our check for -Wcast-qual in CMakeList.txt.

[goatgoose]

I think this change conflicts with #5198?

If we want to continue to support older versions of AWS-LC, I'm not sure we can add this flag. Unless there's a way to check the AWS-LC version first.