Make LTO codegen use a PassManager, rather than a FunctionPassManager, for the
codegen passes. This brings it in to line with clang and llc's codegen setup,
and tidies up the code.

If I understand correctly, adding ModulePasses to a FunctionPassManager is
bogus. It only seems to explode if an added ModulePass depends on a
FunctionPass though, which might be why this code has survived so long.

Fixes <rdar://problem/13386816>.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176977 91177308-0d34-0410-b5e6-96231b3b80d8