[LPM] Use a map from analysis ID to immutable passes in the legacy pass

[LPM] Use a map from analysis ID to immutable passes in the legacy pass
manager to avoid a slow linear scan of every immutable pass and on every
attempt to find an analysis pass.

This speeds up 'check-llvm' on an unoptimized build for me by 15%, YMMV.
It should also help (a tiny bit) other folks that are really
bottlenecked on repeated runs of tiny pass pipelines across small IR
files.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247240 91177308-0d34-0410-b5e6-96231b3b80d8