Rollup merge of #128961 - GKFX:issue-128930-explain-missing-option, r=jieyouxu

Fix #128930: Print documentation of CLI options missing their arg

Fix #128930. Failing to give an argument to CLI options which require it now prints something like:
```
$ rustc --print
error: Argument to option 'print' missing
       Usage:
           --print [crate-name|file-names|sysroot|target-libdir|cfg|check-cfg|calling-conventions|target-list|target-cpus|target-features|relocation-models|code-models|tls-models|target-spec-json|all-target-specs-json|native-static-libs|stack-protector-strategies|link-args|deployment-target]
                               Compiler information to print on stdout
```

compiler/rustc_session/src/config.rs

@@ -1376,7 +1376,7 @@ enum OptionStability {
 
 pub struct RustcOptGroup {
     pub apply: Box<dyn Fn(&mut getopts::Options) -> &mut getopts::Options>,
-    name: &'static str,
+    pub name: &'static str,
     stability: OptionStability,
 }