Merge ref 'dfe1b8c97bcd' from rust-lang/rust

Pull recent changes from https://github.com/rust-lang/rust via Josh.

Upstream ref: dfe1b8c97bcde283102f706d5dcdc3649e5e12e3
Filtered ref: eb856a4
Upstream diff: rust-lang/rust@1be6b13...dfe1b8c

This merge was created using https://github.com/rust-lang/josh-sync.

Author: The rustc-josh-sync Cronjob Bot

src/tests/running.md

@@ -321,6 +321,10 @@ Tests are built on the machine running `x` not on the remote machine.
 Tests which fail to build unexpectedly (or `ui` tests producing incorrect build
 output) may fail without ever running on the remote machine.
 
+There is a default timeout of 30 minutes in case the `remote-test-server`
+cannot be reached by the `x` command. This timeout can be modified by using the
+`TEST_DEVICE_CONNECT_TIMEOUT_SECONDS` environment variable.
+
 ## Testing on emulators
 
 Some platforms are tested via an emulator for architectures that aren't readily available.