Revert "Simplify the pass manager execution logic."
Revert "Simplify the pass manager execution logic."

This reverts commit 9d4d3c8055dac6a92baa1a3977645ae616bad614.

I forgot to finish up changes required to make -Xllvm
-sil-opt-pass-count continue working the way it did, so I'll back that
out until I have those changes as well.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift