[getconf] macos testing fixes

Completed Fixes

  | Fix   | Description                                                                                                                    | Status |
  |-------|--------------------------------------------------------------------------------------------------------------------------------|--------|
  | Fix 1 | Proper errno checking - outputs "undefined" with exit 0 instead of error when sysconf/pathconf returns -1 with errno unchanged | ✅     |
  | Fix 2 | POSIX2_* compatibility aliases (POSIX2_VERSION, POSIX2_C_DEV, POSIX2_LINE_MAX, etc.)                                           | ✅     |
  | Fix 3 | Added missing sysconf variables (PAGESIZE, _POSIX_VERSION, HOST_NAME_MAX, _XOPEN_VERSION, etc.)                                | ✅     |
  | Fix 4 | Fixed confstr output to trim null byte                                                                                         | ✅     |
  | Fix 5 | Clean error message format (no Rust debug output)                                                                              | ✅     |
  | Fix 6 | Handle -v option properly (emit "unsupported specification" error)                                                             | ✅     |
  | Fix 7 | Added POSIX_V6_* confstr variables on macOS                                                                                    | ✅     |

  Files Modified

  - sys/getconf.rs - Main implementation
  - sys/Cargo.toml - Added errno dependency

  Test Results

  All tests pass and outputs match the system getconf:
  - sysconf variables (ARG_MAX, NGROUPS_MAX, PAGESIZE, etc.)
  - POSIX2_* compatibility names
  - "undefined" handling for unsupported variables
  - pathconf variables (NAME_MAX, PATH_MAX, etc.)
  - confstr variables (PATH, POSIX_V6_WIDTH_RESTRICTED_ENVS, etc.)

Author: jgarzik

Cargo.lock

@@ -10,6 +10,7 @@ rust-version.workspace = true
 [dependencies]
 plib = { path = "../plib" }
 clap.workspace = true
+errno.workspace = true
 gettext-rs.workspace = true
 uname = "0.1"
 libc.workspace = true