crypt support for musl libc

Hello, i am trying to upgrade the TXR package in Alpine Linux, which is currently at version 278.

Alpine Linux uses musl libc, and on TXR 291, i encounter some issues with failing tests in "tests/018/crypt.tl".

It seems 3 tests that are supposed to produce errors do not do so:

1) (crypt "a" "b") returns "*"
2) (crypt "a" "$0$") returns "$0UqSJBCvZvN."
3) (crypt "a" "$9$") returns "$9SxH5/IxLdbI"

With TXR 278 that is in Alpine's package repo, those function calls error out as expected.

The source code of musl's implementation of crypt() is available here: https://git.musl-libc.org/cgit/musl/tree/src/crypt?h=v1.2.4

Would it be possible to add support for that to TXR?

Thank you.