[libc++] Use explicit module cache path in tests

[abrachet]

Summary

For reference, this test creates about 1.5G in the cache directory. By default this will go to ~/.cache/clang/ which can fill up quick. This changes the test to put the cache path in lit temp directories. Size considerations aside it makes sense for tests to be hermetic and not touch global system state.

[phosek]

LGTM but I'm not libc++ reviewer so you should wait for LGTM from either @ldionne or @EricWF.

[phosek]

@ldionne ping would it be possible to take a look?

[ldionne]

@abrachet Please don't commit patches to libc++ without having approval from the libc++ review group.

Thanks for wanting to improve the test suite -- this is indeed a slow test that creates a lot of stuff on the side. My main comment is actually whether it would make sense to reuse a modules-cache path in the whole test suite (even across tests)?

[ldionne]

In D127587#3582808, @ldionne wrote:

@abrachet Please don't commit patches to libc++ without having approval from the libc++ review group.

By the way, I'm not scolding, just making sure everybody follows the process :-). Let's have a discussion now that the immediate problem is solved!

[abrachet]

In D127587#3582811, @ldionne wrote:

In D127587#3582808, @ldionne wrote:

@abrachet Please don't commit patches to libc++ without having approval from the libc++ review group.

By the way, I'm not scolding, just making sure everybody follows the process :-). Let's have a discussion now that the immediate problem is solved!

No worries I'm not feeling scolded :) I will wait next time.

In D127587#3582808, @ldionne wrote:

Thanks for wanting to improve the test suite -- this is indeed a slow test that creates a lot of stuff on the side. My main comment is actually whether it would make sense to reuse a modules-cache path in the whole test suite (even across tests)?

Sure I could look into that. I'm not too familiar with libcxx's testing infrastructure, do you reckon that would be added to all of the %{compile_flags} substitutions?