[swift-dev] compiler-rt...Wait wat?

[Ryan Lovelett]

I just noticed that if you do `utils/update-checkout --clone` it pulls
down `compiler-rt`. I have been building Swift from source on Linux for
awhile now. I've never once checked out compiler-rt. Which makes me
wonder if that repository is even in use.

Here is the question: what is the compiler-rt repository used for? Is my
build not working as expected without compiler-rt?