Fix FunctionPropertiesAnalysis updating callsite in 1-BB loop

If the callsite is in a single BB loop, we need to exclude the BB from
the successor set (in which it'd be a member), because that set forms a
boundary at which we stop traversing the CFG, when re-ingesting BBs
after inlining; but after inlining, the callsite BB's new successors
should be visited.

Reviewed By: kazu

Differential Revision: https://reviews.llvm.org/D127178