Revert "Reapply "[compiler-rt] Default to Lit's Internal Shell""
This reverts commit 4b6a597230020282fe94ee6f476a3aad45fbe9aa.
This broke premerge and maybe one PPC bot:
1. https://lab.llvm.org/staging/#/builders/192/builds/10157
2. https://lab.llvm.org/buildbot/#/builders/95/builds/19044