rustc: Show @path usage in stable

The feature was stabilized in rust-lang#66172, but the usage string was not
updated to be shown.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

compiler/rustc_driver/src/lib.rs

@@ -821,7 +821,7 @@ fn usage(verbose: bool, include_unstable_options: bool, nightly_build: bool) {
     } else {
         "\n    --help -v           Print the full set of options rustc accepts"
     };
-    let at_path = if verbose && nightly_build {
+    let at_path = if verbose {
         "    @path               Read newline separated options from `path`\n"
     } else {
         ""