rust: builds failing for 10.8 and earlier; related to openssl3 migration

[mascguy (Christopher Nielsen)]

During the initial bootstrap phase of the build, the embedded binary for cargo fails, due to being linked to openssl11:

Building rustbuild
running: /opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_lang_rust/rust/work/cargo-1.60.0-x86_64-apple-darwin/cargo/bin/cargo build --manifest-path /opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_lang_rust/rust/work/rustc-1.61.0-src/src/bootstrap/Cargo.toml --verbose --verbose --offline
dyld: Library not loaded: /opt/local/libexec/openssl11/lib/libssl.1.1.dylib
  Referenced from: /opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_lang_rust/rust/work/cargo-1.60.0-x86_64-apple-darwin/cargo/bin/cargo
  Reason: image not found

It's not clear what the right/best approach is to fixing this, though. (A quick fix would be to add a temporary build dep on openssl11, but that seems like a hack at best.)

​https://ports.macports.org/port/rust/details/