Check exit status of subcommands spawned by rustc_tools_util

[dtolnay]

The git commands git rev-parse --short HEAD and git log -1 --date=short --pretty=format:%cd that clippy runs from its build script might fail with "fatal: not a git repository (or any of the parent directories): .git" if clippy is being built from a source tarball rather than a git repository. That message is written by git to stderr, and nothing is written to stdout.

For clippy-driver --version this PR wouldn't make a difference because it treats empty stdout and failed spawns (git is not installed) identically:

rust-clippy/rustc_tools_util/src/lib.rs

Lines 35 to 42 in 7ac242c

	println!(
	"cargo:rustc-env=GIT_HASH={}",
	$crate::get_commit_hash().unwrap_or_default()
	);
	println!(
	"cargo:rustc-env=COMMIT_DATE={}",
	$crate::get_commit_date().unwrap_or_default()
	);

But other users of rustc_tools_util should be able to expect that the distinction between Some and None is meaningful. They shouldn't need extra code to handle None vs Some-and-empty vs Some-and-nonempty.

---

changelog: none

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[flip1995]

@bors r+

Thanks!

[bors]

📌 Commit 234ea1f has been approved by flip1995

It is now in the queue for this repository.

[bors]

⌛ Testing commit 234ea1f with merge e611c8e...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing e611c8e to master...