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/codemap.rs

@@ -453,7 +453,7 @@ impl CodeMap {
     }
 
     pub fn get_filemap(&self, filename: &str) -> Rc<FileMap> {
-        for fm in self.files.borrow().iter() {
+        for fm in &*self.files.borrow() {
             if filename == fm.name {
                 return fm.clone();
             }
@@ -477,7 +477,7 @@ impl CodeMap {
         // The number of extra bytes due to multibyte chars in the FileMap
         let mut total_extra_bytes = 0;
 
-        for mbc in map.multibyte_chars.borrow().iter() {
+        for mbc in &*map.multibyte_chars.borrow() {
             debug!("{}-byte char at {:?}", mbc.bytes, mbc.pos);
             if mbc.pos < bpos {
                 // every character is at least one byte, so we only