LibreSSL extension (optional)

CMake option: FUN_WITH_LIBRESSL=ON
Purpose: provide small crypto helpers backed by LibreSSL’s libcrypto. Includes md5, sha256, sha512, ripemd160 helpers under libressl_* names.
Homepage: https://www.libressl.org/

Build notes:

Requires system LibreSSL development headers and libcrypto. The build detects LibreSSL directly (via pkg-config or standard include/lib locations) and links to libcrypto from LibreSSL — it does not require OpenSSL to be installed.
When disabled, the builtins below evaluate to empty strings to mirror optionality behavior across extensions.

Function: libressl_md5(data:string) -> string (lowercase hex).
Function: libressl_sha256(data:string) -> string (lowercase hex).
Function: libressl_sha512(data:string) -> string (lowercase hex).
Function: libressl_ripemd160(data:string) -> string (lowercase hex).
Opcodes: OP_LIBRESSL_MD5, OP_LIBRESSL_SHA256, OP_LIBRESSL_SHA512, OP_LIBRESSL_RIPEMD160 (internal mappings for the functions above).

Configure: cmake -S . -B build -DFUN_WITH_LIBRESSL=ON
Build: cmake --build build --target fun
Run examples:
- ./build/fun examples/crypto/libressl_md5.fun
- ./build/fun examples/crypto/libressl_sha256.fun
- ./build/fun examples/crypto/libressl_sha512.fun
- ./build/fun examples/crypto/libressl_ripemd160.fun

md5(abc) = 900150983cd24fb0d6963f7d28e17f72
md5("") = d41d8cd98f00b204e9800998ecf8427e
sha256(abc) = ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad
sha256("") = e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
sha512(abc) = ddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f
sha512("") = cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e
ripemd160(abc) = 8eb208f7e05d987a9b044a8e98c6b087f15a0bfc
ripemd160("") = 9c1185a5c5e9fc54612808977ee8f548b2258d31

The functions accept any Fun value; non-strings are coerced via to_string semantics by the VM before hashing.
On some platforms, RIPEMD-160 may not be available; in that case the helper returns an empty string.
If your system installs LibreSSL headers under /usr/include/libressl, CMake will automatically add this directory to the include path so that #include <libressl/openssl/...> resolves correctly.