Auto merge of #60435 - Centril:rollup-aa5lmuw, r=Centril

Rollup of 7 pull requests

Successful merges:

 - #60287 (Use references for variances_of)
 - #60327 (Search for incompatible universes in borrow errors)
 - #60330 (Suggest using an inclusive range instead of an exclusive range when the endpoint overflows by 1)
 - #60366 (build-gcc: Create missing cc symlink)
 - #60369 (Support ZSTs in DispatchFromDyn)
 - #60404 (Implement `BorrowMut<str>` for `String`)
 - #60417 (Rename hir::ExprKind::Use to ::DropTemps and improve docs.)

Failed merges:

r? @ghost

Author: bors

src/ci/docker/dist-x86_64-linux/build-gcc.sh

@@ -32,6 +32,7 @@ hide_output ../gcc-$GCC/configure \
     --enable-languages=c,c++
 hide_output make -j10
 hide_output make install
+ln -s gcc /rustroot/bin/cc
 
 cd ..
 rm -rf gcc-build

src/liballoc/str.rs

@@ -28,7 +28,7 @@
 // It's cleaner to just turn off the unused_imports warning than to fix them.
 #![allow(unused_imports)]
 
-use core::borrow::Borrow;
+use core::borrow::{Borrow, BorrowMut};
 use core::str::pattern::{Pattern, Searcher, ReverseSearcher, DoubleEndedSearcher};
 use core::mem;
 use core::ptr;
@@ -190,6 +190,14 @@ impl Borrow<str> for String {
     }
 }
 
+#[stable(feature = "string_borrow_mut", since = "1.36.0")]
+impl BorrowMut<str> for String {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut str {
+        &mut self[..]
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ToOwned for str {
     type Owned = String;