rollup merge of #21830: japaric/for-cleanup

Conflicts:
	src/librustc/metadata/filesearch.rs
	src/librustc_back/target/mod.rs
	src/libstd/os.rs
	src/libstd/sys/windows/os.rs
	src/libsyntax/ext/tt/macro_parser.rs
	src/libsyntax/print/pprust.rs
	src/test/compile-fail/issue-2149.rs

src/libsyntax/parse/parser.rs

@@ -2713,7 +2713,7 @@ impl<'a> Parser<'a> {
         match self.token {
             token::Eof => {
                 let open_braces = self.open_braces.clone();
-                for sp in open_braces.iter() {
+                for sp in &open_braces {
                     self.span_help(*sp, "did you mean to close this delimiter?");
                 }
                 // There shouldn't really be a span, but it's easier for the test runner
@@ -5207,7 +5207,7 @@ impl<'a> Parser<'a> {
             Some(i) => {
                 let mut err = String::from_str("circular modules: ");
                 let len = included_mod_stack.len();
-                for p in included_mod_stack[i.. len].iter() {
+                for p in &included_mod_stack[i.. len] {
                     err.push_str(&p.display().as_cow()[]);
                     err.push_str(" -> ");
                 }
@@ -5452,7 +5452,7 @@ impl<'a> Parser<'a> {
                     seq_sep_trailing_allowed(token::Comma),
                     |p| p.parse_ty_sum()
                 );
-                for ty in arg_tys.into_iter() {
+                for ty in arg_tys {
                     args.push(ast::VariantArg {
                         ty: ty,
                         id: ast::DUMMY_NODE_ID,