rollup merge of rust-lang#27674: zaeleus/ios-imports

See rust-lang#27590 (comment).

src/libstd/rand/os.rs

@@ -182,12 +182,12 @@ mod imp {
 
 #[cfg(target_os = "ios")]
 mod imp {
-    use prelude::v1::*;
+    #[cfg(stage0)] use prelude::v1::*;
 
     use io;
     use mem;
     use rand::Rng;
-    use libc::{c_int, c_void, size_t};
+    use libc::{c_int, size_t};
 
     /// A random number generator that retrieves randomness straight from
     /// the operating system. Platform sources:

src/libstd/sys/unix/backtrace.rs

@@ -107,6 +107,8 @@ use sys_common::backtrace::*;
 #[cfg(all(target_os = "ios", target_arch = "arm"))]
 #[inline(never)]
 pub fn write(w: &mut Write) -> io::Result<()> {
+    use mem;
+
     extern {
         fn backtrace(buf: *mut *mut libc::c_void,
                      sz: libc::c_int) -> libc::c_int;
@@ -121,7 +123,7 @@ pub fn write(w: &mut Write) -> io::Result<()> {
     try!(writeln!(w, "stack backtrace:"));
     // 100 lines should be enough
     const SIZE: usize = 100;
-    let mut buf: [*mut libc::c_void; SIZE] = unsafe {mem::zeroed()};
+    let mut buf: [*mut libc::c_void; SIZE] = unsafe { mem::zeroed() };
     let cnt = unsafe { backtrace(buf.as_mut_ptr(), SIZE as libc::c_int) as usize};
 
     // skipping the first one as it is write itself