Add support for shell argfiles

compiler/rustc_session/src/options.rs

@@ -1875,6 +1875,8 @@ written to standard error output)"),
                      query-blocked, incr-cache-load, incr-result-hashing, query-keys, function-args, args, llvm, artifact-sizes"),
     share_generics: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "make the current crate share its generic instantiations"),
+    shell_argfiles: bool = (false, parse_bool, [UNTRACKED],
+        "allow argument files to be specified with POSIX \"shell-style\" argument quoting"),
     show_span: Option<String> = (None, parse_opt_string, [TRACKED],
         "show spans for compiler debugging (expr|pat|ty)"),
     simulate_remapped_rust_src_base: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],