Auto merge of #53996 - sekineh:thumb-run, r=japaric

[CI] Run a `thumbv7m-none-eabi` binary using `qemu-system-arm` [IRR-2018-embedded]

## What's included?

- Run a `thumbv7m-none-eabi` binary using `qemu-system-arm`
- We are using `cortex-m-rt = "=0.5.4"` which does not use `proc_macro`.
(reason: stage2 build of rustc does not work well with `proc_macro` in `run-make` phase.)
- We are using GNU LD for now.

## Blocker

All resolved.
- ~[Waiting] `#[panic_handler]` is not available in stable.~
  - [Merged] https://github.com/rust-lang/rust/pull/53619
- ~[Waiting] https://github.com/japaric/lm3s6965evb: does not compile on stable.~
  - [OK] dependent crate ~`panic-abort`~ `panic-halt`: already moved to use `#[panic_handler]`.

## Update

`#[panic_handler]` will be stabilized in Rust 1.30.

CC @kennytm @jamesmunns @nerdyvaishali
7 jobs for master in 1 minute and 43 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #4763
build

00:01:43

 
  Test
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code_quality
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container_scanning
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dependency_scanning
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license_management
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sast
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Name Stage Failure
failed
build Build
Skipping Git submodules setup
$ # Auto DevOps variables and functions # collapsed multi-line command
$ setup_docker
$ build
Logging to GitLab Container Registry with CI credentials...
WARNING! Using --password via the CLI is insecure. Use --password-stdin.
Warning: failed to get default registry endpoint from daemon (Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?). Using system default: https://index.docker.io/v1/
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
ERROR: Job failed: exit code 1