fix: crypto implementations not being compiled

[RokasPuzonas]

Because of the LIBSSH2_CRYPTO_C ifdef at the top of src/openssl.c, src/mbedtls.c, src/libgcrypt.c, src/wincng.c these crypto backends couldn't be used.

It would fail with these kinds of error:

error: undefined symbol: _libssh2_mbedtls_random
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/2cb63cf0ca6e9aa751f1df0888da2261/channel.o/):.text
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/28a72c5e23a642bd413157731ed57289/kex.o/):.text
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/ae98866eb50c1eab86ef8af28da13486/transport.o/):.text
error: undefined symbol: _libssh2_mbedtls_cipher_init
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/8e6643d4a607c887ad66270bdc2bb433/crypt.o/):.text
error: undefined symbol: _libssh2_mbedtls_cipher_crypt
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/8e6643d4a607c887ad66270bdc2bb433/crypt.o/):.text
error: undefined symbol: _libssh2_mbedtls_cipher_dtor
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/8e6643d4a607c887ad66270bdc2bb433/crypt.o/):.text
error: undefined symbol: _libssh2_mbedtls_init
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/a97e21cd704e51c71c5c9fc294fe88b6/global.o/):.text
error: undefined symbol: _libssh2_mbedtls_free
    note: referenced by .zig-cache/o/11843e63979650ec3e09dac0b545db56/libssh2.a(.zig-cache/o/a97e21cd704e51c71c5c9fc294fe88b6/global.o/):.text

...

FYI. After some additional investigating I noticed that this LIBSSH2_CRYPTO_C ifdef doesn't exist in the master branch of libssh2. Because it was removed with this commit libssh2/libssh2@e0681cd. So when upgrading past libssh2-1.11.1 this part will need to be updated again.

Maybe as a future improvement CI/CD needs to be setup for this, so this kind of bug doesn't reoccur?

[hamptokr]

Thanks for the PR! I had pinned the upstream to 1.11.1 and then used master's cmake as a guide, which led to the error here. In future versions crypto.c will be removed and we will have to add this back 💡