[FunctionAttrs] Separate another chunk of the logic for functionattrs

[FunctionAttrs] Separate another chunk of the logic for functionattrs
from its pass harness by providing a lambda to query for AA results.

This allows the legacy pass to easily provide a lambda that uses the
special helpers to construct function AA results from a legacy CGSCC
pass. With the new pass manager (the next patch) the lambda just
directly wraps the intuitive query API.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251715 91177308-0d34-0410-b5e6-96231b3b80d8