Rollup of 4 pull requests

src/bootstrap/build/sanity.rs

@@ -79,7 +79,7 @@ pub fn check(build: &mut Build) {
         }
 
         // Make sure musl-root is valid if specified
-        if target.contains("musl") {
+        if target.contains("musl") && target.contains("x86_64") {
             match build.config.musl_root {
                 Some(ref root) => {
                     if fs::metadata(root.join("lib/libc.a")).is_err() {

src/doc/book/vectors.md

@@ -115,6 +115,36 @@ for i in v {
 }
 ```
 
+Note: You cannot use the vector again once you have iterated by taking ownership of the vector.
+You can iterate the vector multiple times by taking a reference to the vector whilst iterating. 
+For example, the following code does not compile.
+
+```rust,ignore
+let mut v = vec![1, 2, 3, 4, 5];
+
+for i in v {
+    println!("Take ownership of the vector and its element {}", i);
+}
+
+for i in v {
+    println!("Take ownership of the vector and its element {}", i);
+}
+```
+
+Whereas the following works perfectly,
+
+```rust
+let mut v = vec![1, 2, 3, 4, 5];
+
+for i in &v {
+    println!("This is a reference to {}", i);
+}
+
+for i in &v {
+    println!("This is a reference to {}", i);
+}
+```
+
 Vectors have many more useful methods, which you can read about in [their
 API documentation][vec].
 

src/libcore/str/mod.rs

@@ -1095,8 +1095,6 @@ fn eq_slice(a: &str, b: &str) -> bool {
 /// faster than comparing each byte in a loop.
 #[inline]
 unsafe fn cmp_slice(a: &str, b: &str, len: usize) -> i32 {
-    // NOTE: In theory n should be libc::size_t and not usize, but libc is not available here
-    #[allow(improper_ctypes)]
     extern { fn memcmp(s1: *const i8, s2: *const i8, n: usize) -> i32; }
     memcmp(a.as_ptr() as *const i8, b.as_ptr() as *const i8, len)
 }

src/libstd/build.rs

@@ -28,7 +28,7 @@ fn main() {
     }
 
     if target.contains("unknown-linux") {
-        if target.contains("musl") {
+        if target.contains("musl") && target.contains("x86_64") {
             println!("cargo:rustc-link-lib=static=unwind");
         } else {
             println!("cargo:rustc-link-lib=dl");

src/test/rustdoc/issue-27362.rs

@@ -10,6 +10,7 @@
 
 // aux-build:issue-27362.rs
 // ignore-cross-compile
+// ignore-test This test fails on beta/stable #32019
 
 extern crate issue_27362;
 pub use issue_27362 as quux;