Shorten paths to auxiliary files created by tests

[petrochenkov]

I'm hitting issues with long file paths to object files created by the test suite, similar to #45103 (comment).

If we look at the object file path in #45103 we can see that the patch contains of few components:

specialization-cross-crate-defaults.stage2-x86_64-pc-windows-gnu.run-pass.libaux\specialization_cross_crate_defaults.specialization_cross_crate_defaults0.rust-cgu.o

=>

1. specialization-cross-crate-defaults // test name, required
2. stage2 // stage disambiguator, required
3. x86_64-pc-windows-gnu // target disambiguator, required
4. run-pass // mode disambiguator, rarely required
5. libaux // suffix, can be shortened
6. specialization_cross_crate_defaults // required, there may be several libraries in the directory
7. specialization_cross_crate_defaults0 // codegen unit name, can be shortened?
8. rust-cgu // suffix, can be shortened?
9. o // object file extension

This patch addresses items 4, 5 and 8.
libaux is shortened to aux, rust-cgu is shortened to rcgu, mode disambiguator is omitted unless it's necessary (for pretty-printing and debuginfo tests, see 38d26d8)

I haven't touched names of codegen units though (specialization_cross_crate_defaults0).
Is it useful for them to have descriptive names including the crate name, as opposed to just 0 or cgu0 or something?

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

@bors: r+

Thanks!

One possible strategy could be a cargo-like strategy where everything is hashed but a descriptive name remains in front for debugging

[bors]

📌 Commit d588f93 has been approved by alexcrichton

[Zoxc]

You could drop x86_64-pc-windows-gnu too since these files are created inside build\x86_64-pc-windows-gnu.

[petrochenkov]

@Zoxc
build\x86_64-pc-windows-gnu refers to the host triple, but disambiguator x86_64-pc-windows-gnu refers to a target triple.
If tests are run from one x86_64-pc-windows-gnu host for several targets, they will all end up in build\x86_64-pc-windows-gnu.
(In principle the disambiguator can be omitted when target == host though, leaving only cross-compiled paths long.)

[bors]

⌛ Testing commit d588f93 with merge 16e9b9f...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 16e9b9f to master...