sign binaries on macOS

[riptl]

consider signing the Rust + LLVM bins on macOS to avoid "unverified developer" warnings.

Solana could either create their own CA and ask users to import,
or buy a DigiCert Signing Cert and use the codesign command-line tool in CI

[riptl]

example

--- stderr
dyld[20253]: Library not loaded: '@rpath/librustc_driver-1095a6ea14c736d2.dylib'
  Referenced from: '/Users/richard/.cache/solana/v1.29/sbf-tools/rust/bin/rustc'
  Reason: tried: '/Users/richard/.cache/solana/v1.29/sbf-tools/rust/bin/../lib/librustc_driver-1095a6ea14c736d2.dylib' (code signature in <ED677311-B9C4-37E3-BFCB-76DB677F8117> '/Users/richard/.cache/solana/v1.29/sbf-tools/rust/lib/librustc_driver-1095a6ea14c736d2.dylib' not valid for use in process: library load disallowed by system policy), '/Users/richard/.cache/solana/v1.29/sbf-tools/rust/bin/../lib/librustc_driver-1095a6ea14c736d2.dylib' (code signature in <ED677311-B9C4-37E3-BFCB-76DB677F8117> '/Users/richard/.cache/solana/v1.29/sbf-tools/rust/lib/librustc_driver-1095a6ea14c736d2.dylib' not valid for use in process: library load disallowed by system policy), '/Users/richard/.rustup/toolchains/sbf/lib/librustc_driver-1095a6ea14c736d2.dylib' (code signature in <ED677311-B9C4-37E3-BFCB-76DB677F8117> '/Users/richard/.cache/solana/v1.29/sbf-tools/rust/lib/librustc_driver-1095a6ea14c736d2.dylib' not valid for use in process: library load disallowed by system policy), '/Users/richard/lib/librustc_driver-1095a6ea14c736d2.dylib' (no such file), '/usr/local/lib/librustc_driver-1095a6ea14c736d2.dylib' (no such file), '/usr/lib/librustc_driver-1095a6ea14c736d2.dylib' (no such file)

[ksolana]

Is this still an issue?