[compiler-rt] Reapply "[compiler-rt] Default to Lit's Internal Shell" (PR #168232)

[Daniel Thornburgh via llvm-commits]

mysterymath wrote:

> It was reverted four hours ago. [cf0909e](https://github.com/llvm/llvm-project/commit/cf0909e95fcfa20f7d8aeb312c05b29aafb9b62f)

Hm? That commit is for the *original* PR; this is a reland of that PR.

https://github.com/llvm/llvm-project/pull/168232