Auto merge of #1097 - RalfJung:rustup, r=RalfJung

bump Rust for exact_div fix

rust-version

@@ -1 +1 @@
-4787e97475de6be9487e3d9255a9c2d3c0bf9252
+f577b0ef6e637ab7a6095cdfe0b51fa3faf97050

tests/compile-fail/exact_div3.rs

@@ -1,5 +1,5 @@
 #![feature(core_intrinsics)]
 fn main() {
     // signed divison with a remainder
-    unsafe { std::intrinsics::exact_div(-19i8, 2); } //~ ERROR 237 cannot be divided by 2 without remainder
+    unsafe { std::intrinsics::exact_div(-19i8, 2); } //~ ERROR -19 cannot be divided by 2 without remainder
 }