Fix argument parsing in compiletest for quoted strings

[JumpiiX]

Fixes compiletest breaking when using quoted arguments like --cfg 'feature="my app"' in compile-flags or custom diff tools.

Uses proper shell argument parsing instead of naive whitespace splitting.

Closes #132599

[rustbot]

Some changes occurred in src/tools/compiletest

cc @jieyouxu

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[rustbot]

r? @wesleywiser

rustbot has assigned @wesleywiser.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @jieyouxu, @oli-obk, @wesleywiser, bootstrap
• @jieyouxu, @oli-obk, @wesleywiser, bootstrap expanded to 8 candidates
• Random selection from Mark-Simulacrum, clubby789, jieyouxu, wesleywiser

[JumpiiX]

@wesleywiser I've narrowed this fix to only handle custom diff commands with quoted arguments (the original issue).

I initially tried using shlex for all argument parsing, but this breaks ~50-90 existing tests that use unquoted --cfg key=value syntax in their compile-flags directives.

Two options:

1. Current approach: Only fix diff command parsing, leave compile-flags as-is for backward compatibility
2. Alternative: Update all affected tests to use proper shell quoting (would touch 50+ test files)

Which approach would you prefer? Happy to go either way, just wanted to keep the PR focused initially.

[jieyouxu]

View changes since the review

Remark: so actually, this case I care less about, properly splitting diff command stuff is "nice-to-have" for users on custom diff tools but this is not correctness-critical

[fmease]

I initially tried using shlex for all argument parsing, but this breaks ~50-90 existing tests that use unquoted --cfg key=value syntax in their compile-flags directives.

Two options:

1. Current approach: Only fix diff command parsing, leave compile-flags as-is for backward compatibility
2. Alternative: Update all affected tests to use proper shell quoting (would touch 50+ test files)

Which approach would you prefer? Happy to go either way, just wanted to keep the PR focused initially.

Personally speaking, I vote for option (2), shlex everywhere, update all tests and be done with it.

[rust-bors]

☔ The latest upstream changes (presumably #158212) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.