Add path prefixes back when compiling clippy_dev and lintcheck

[Alexendoo]

cargo dev and cargo lintcheck use --manifest-path to select the package to compile, with this Cargo changes the CWD to the package's containing directory meaning paths in diagnostics start from e.g. src/ instead of clippy_dev/src/

Lintcheck uses a --remap-path-prefix trick when linting crates to re-add the directory name in diagnostics:

rust-clippy/lintcheck/src/main.rs

Lines 93 to 94 in 5ead90f

	// `src/lib.rs` -> `target/lintcheck/sources/crate-1.2.3/src/lib.rs`
	let remap_relative = format!("={}", self.path.display());

rust-clippy/lintcheck/src/main.rs

Lines 102 to 103 in 5ead90f

	"--remap-path-prefix",
	&remap_relative,

It works well as far as I can tell, when absolute paths appear they stay absolute and do not have the prefix added

profile-rustflags allows us to set per package RUSTFLAGS in order to use the same trick on the clippy_dev and lintcheck packages themselves

Now when you run into warnings/errors the filename will be correctly clickable

Before

error[E0425]: cannot find value `moo` in this scope
  --> src/lib.rs:41:5
   |
41 |     moo;
   |     ^^^ not found in this scope

After

error[E0425]: cannot find value `moo` in this scope
  --> clippy_dev/src/lib.rs:41:5
   |
41 |     moo;
   |     ^^^ not found in this scope

r? @flip1995

changelog: none

[flip1995]

Makes sense. Thanks!

@bors r+

[bors]

📌 Commit 8225f2a has been approved by flip1995

It is now in the queue for this repository.

[bors]

⌛ Testing commit 8225f2a with merge f2deab3...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing f2deab3 to master...