Move std::test into core or change the way coretest works

[brson]

Running tests requires linking to std, where the test runner lives. core has a huge hack in it to allow it to link to std when building with --test.

When building core tests (an executable), core links to std, which then links to the actual core shared library. As a result coretest actually includes two entire copies of core at runtime. The tests are exercising the core code compiled into the executable, and std is exercising the core library.

This caused a confusing problem with the TLS tests which use function addresses as keys, because std and coretest were using two different functions.

Two solutions

• move std::test to core
• move core tests to their own crate

[bblum]

This can be worked around for TLS; it just means that any user of TLS within core has to completely cheat.

[z0w0]

I think it's a good idea to have it in core. Really, any functionality that is in the compiler should be supported by core.

[brson]

This is also a problem for build times, since we compile core twice to test it.

[catamorphism]

Not really a backwards-compatibility bug. Just a bug, maybe?

[brson]

extra::test has several dependencies from extra that I'm not interested in moving into std, sadly. maybe some of them could be code-duplicated in std or sneakily exported from std::unstable and then reexported from extra. it uses at least term and sort. probably workcache someday too. the status quo seems to be working out ok for us right now so I'm not too worried about it atm.

[huonw]

Triage: we're still using the weird work-arounds since extra::test is still extra::test.

[emberian]

I think what we have today is fine, we should close this.

[brson]

Agree, there's no going back now.