_hmac module bypasses --with-builtin-hashlib-hashes by embedding all HACL hash implementations

Bug report

Bug description:

When configuring Python with e.g. --with-builtin-hashlib-hashes=blake2 to build only the blake2 builtin hash module, the _hmac module is still unconditionally built and embeds all HACL hash implementations (MD5, SHA1, SHA2, SHA3, Blake2).

While in these cases the excluded hashes are not built as extension modules, since they are compiled into _hmac, then md5 and other disabled digests can still be computed

>>> import _hmac
>>> _hmac.compute_digest(b'key', b'msg', 'md5')
b'\x18\xe3T\x8cY\xad@\xdd\x03\x90{z\xee\xe7\x1dg'

Not sure if that is intended behaviour or an oversight but it seems to defeat the purpose of excluding specific hashes. Also increases the size of _hmac substantially. Discovered it when working on a FIPS build.

On our FIPS build I opted for completely disabling _hmac in this case (FIPS builds only utilize OpenSSL anyway for hmac)

CPython versions tested on:

3.15, 3.14

Operating systems tested on:

Linux

从链接的 configure.ac 部分以及 Makefile.pre.in 中的 HACL 源代码条目开始。使用 --with-builtin-hashlib-hashes=blake2 配置 CPython，进行构建，并重现 _hmac.compute_digest(..., 'md5') 的行为。当 _hmac 遵循选定的哈希配置，且被排除的实现不再嵌入时，即视为完成。