Auto merge of #153957 - xonx4l:stdarch-verify, r=Kobzol,bjorn3

Add bootstrap step for stdarch-verify



This PR hooks `library/stdarch/crates/stdarch-verify` crate into the bootstrap test runner as a step, so that we can run the stdarch-verify suite via x.py test.

Changes :
-> Added StdarchVerify in `src/bootstrap/src/core/build_steps/test.rs`
-> Added `test::StdarchVerify`  in `src/bootstrap/src/core/builder/mod.rs`

Tests:
-> Running `./x.py test library/stdarch/crates/stdarch-verify`  builds compiler and std  successfully.
-> All  three integration tests Passes:
     tests/arm.rs 
     tests/mips.rs 
     tests/x86-intel.rs 
-> Doc tests for `stdarch_verify` also Passes.

r? @Kobzol

try-job: x86_64-gnu-distcheck

Author: bors