Fix problem with inserting FunctionPasses that depend on ImmutablePasses

Fix problem with inserting FunctionPasses that depend on ImmutablePasses
(e.g., LICM) into FunctionPassManagers. The problem is that we were
using a C-style cast to cast required analysis passes to PassClass*, but
if it's a FunctionPassManager, and the required analysis pass is an
ImmutablePass, the types aren't really compatible, so the C-style cast
causes a crash.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15140 91177308-0d34-0410-b5e6-96231b3b80d8