Add --print-env option to c3c

[Adversing]

Add --print-env option to c3c to print build environment in JSON format as requested in #1832

[lerno]

When wired up it produces the following for compile:

{
  "c3c": {
    "version": "0.6.7",
    "stdlib": "/Users/lerno/Projects/c3c/cmake-build-debug-latest/../lib/",
    "c3c_exe": "../../cmake-build-debug-latest/c3c"
  },
  "project": {
    "path": "/Users/lerno/Projects/c3c/resources/testproject",
    "target": "(null)"
  },
  "environment": {
    "system_path": "/opt/homebrew/bin:/opt/homebrew/sbin:/opt/local/bin:/opt/local/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/X11/bin:/Library/Apple/usr/bin:/Applications/Xcode.app/Contents/Developer/../Applications/Application Loader.app/Contents/MacOS/itms/bin",
    "os": "UNKNOWN",
    "variables": {
      "env::POSIX": false,
      "env::win32": false,
      "LIBC": false
    }
  }
}

1. It's on MacOS, so the target detection is incorrect.
2. I don't have a project, so it should possibly list matching files and such, but not a project.

[lerno]

Ping

[Adversing]

Apologies, I can't work on it at the moment. If anyone else wants to take it on, please feel free.

[lerno]

It's fine, I can complete it later.