…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#124655 (Add `-Zfixed-x18`)
 - rust-lang#125693 (Format all source files in `tests/coverage/`)
 - rust-lang#125700 (coverage: Avoid overflow when the MC/DC condition limit is exceeded)
 - rust-lang#125705 (Reintroduce name resolution check for trying to access locals from an inline const)
 - rust-lang#125708 (tier 3 target policy: clarify the point about producing assembly)
 - rust-lang#125715 (remove unneeded extern crate in rmake test)
 - rust-lang#125719 (Extract coverage-specific code out of `compiletest::runtest`)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#125719 - Zalathar:run-coverage, r=jieyouxu

Extract coverage-specific code out of `compiletest::runtest`

I had been vaguely intending to do this for a while, but seeing rust-lang#89475 on the compiletest dashboard inspired me to actually go and do it.

This moves a few hundred lines of coverage-specific code out of the main module, making navigation a bit easier. There is still a small amount of coverage-specific logic in broader functions in that module, since it can't easily be moved.

This is just cut-and-paste plus fixing visibility and imports, so no functional changes.

I also removed the unit test for anonymizing line numbers in MC/DC reports, as foreshadowed by the comment I wrote when adding it. That functionality is now adequately exercised by the actual snapshot tests for MC/DC coverage.

(Removing the test now avoids the need to move it, or to make the function it calls visible.)