Auto merge of #1117 - rust-lang:rustup, r=RalfJung

Rustup to rustc 1.42.0-nightly (9ff30a781 2019-12-21)

rust-version

@@ -1 +1 @@
-a605441e049f0b6d5f7715b94b8ac4662fd7fcf6
+9ff30a7810c586819a78188c173a7b74adbb9730

tests/compile-fail/stacked_borrows/illegal_write6.rs

@@ -7,6 +7,6 @@ fn main() {
 fn foo(a: &mut u32, y: *mut u32) -> u32 {
     *a = 1;
     let _b = &*a;
-    unsafe { *y = 2; } //~ ERROR: borrow stack
+    unsafe { *y = 2; } //~ ERROR: not granting access to tag
     return *a;
 }