Use the existing LLVM GitInfo for checking rebuilds

[cuviper]

Fixes #59565

[rust-highfive]

r? @alexcrichton

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[cuviper]

r? @Mark-Simulacrum

[cuviper]

Hmm, except "dev" builds ignore git, which isn't what we want for LLVM...

rust/src/bootstrap/config.rs

Lines 649 to 650 in fc8581d

	let default = config.channel == "dev";
	config.ignore_git = ignore_git.unwrap_or(default);

[Mark-Simulacrum]

I'm not sure, but perhaps we could add an argument to GitInfo new or something along those lines that would usually be the config.ignore_git but for LLVM just true.

[cuviper]

I just pushed a commit which roughly does that -- passing ignore_git: bool instead of &Config, always false for LLVM dirs.

[Mark-Simulacrum]

Looks good to me! Bumping priority since this fixes a regression.

@bors r+ p=1

[bors]

📌 Commit 49b65e6 has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 49b65e6 with merge cee58fd...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: Mark-Simulacrum
Pushing cee58fd to master...