Auto merge of #53190 - sekineh:thumb-cortex-m, r=jamesmunns

Add crate build test for `thumb*` targets. [IRR-2018-embedded]

## Summary

This PR adds `run-make` test that compiles `cortex-m` crate for all supported `thumb*-none-*` targets using `cargo` and stage2 `rustc`.

- Supported `thumb*-none-*` targets:
  - thumbv6m-none-eabi (Bare Cortex-M0, M0+, M1)
  - thumbv7em-none-eabi (Bare Cortex-M4, M7)
  - thumbv7em-none-eabihf (Bare Cortex-M4F, M7F, FPU, hardfloat)
  - thumbv7m-none-eabi (Bare Cortex-M3)

## How to run & Example output
I tested locally and all targets succeeded like below:
```
./x.py clean
./x.py test --target thumbv6m-none-eabi,thumbv7em-none-eabi,thumbv7em-none-eabihf,thumbv7m-none-eabi src/test/run-make
```
```
Check compiletest suite=run-make mode=run-make (x86_64-unknown-linux-gnu -> thumbv6m-none-eabi)

running 5 tests
.....
test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
```

## How to re-run

Remove `stamp` file for the test run.
```
rm build/x86_64-unknown-linux-gnu/test/run-make/thumb-none-cortex-m/stamp
```
Then run `test`
```
./x.py test --target thumbv6m-none-eabi,thumbv7em-none-eabi,thumbv7em-none-eabihf,thumbv7m-none-eabi src/test/run-make
(snip)
running 5 tests
iiii.
test result: ok. 1 passed; 0 failed; 4 ignored; 0 measured; 0 filtered out
```

## Artifacts

You can examine the artifacts under the directory below:
```
sekineh@sekineh-VirtualBox:~/rustme10$ ls -l build/x86_64-unknown-linux-gnu/test/run-make/thumb-none-cortex-m/thumb-none-cortex-m/
total 4
drwxrwxr-x 7 sekineh sekineh 4096  8月 14 22:40 cortex-m
```
where `build/x86_64-unknown-linux-gnu/test/run-make/thumb-none-cortex-m/thumb-none-cortex-m/` is came from TMPDIR variable.

## Other notes

For `test.rs` modification, I used the same logic as:
- https://github.com/rust-lang/rust/blame/d8b3c830fbcdd14d085209a8dcc3399151f3286a/src/bootstrap/dist.rs#L652-L657
```
            if builder.no_std(target) == Some(true) {
                // the `test` doesn't compile for no-std targets
                builder.ensure(compile::Std { compiler, target });
            } else {
                builder.ensure(compile::Test { compiler, target });
            }
```
It is a useful snippet when adding `no_std` support to `src/bootstrap` code.

CC @kennytm @jamesmunns @nerdyvaishali

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