Auto merge of #43281 - mmatyas:remotetest_env, r=alexcrichton
Auto merge of #43281 - mmatyas:remotetest_env, r=alexcrichton

Allow remote testing remotely when `TEST_DEVICE_ADDR` is set

Remote testing was added in #41268, but at the moment it's only enabled if QEMU is also available or we're testing Android. This patch also allows remote testing if the environment variable `TEST_DEVICE_ADDR` is set, as required by `remote-test-client` [[1](https://github.com/rust-lang/rust/blob/master/src/tools/remote-test-client/src/main.rs#L28), [2](https://github.com/rust-lang/rust/blob/master/src/tools/remote-test-client/src/main.rs#L61)]

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