[StackSafety] Run ThinLTO

Summary:
ThinLTO linking runs dataflow processing on collected
function parameters. Then StackSafetyGlobalInfoWrapperPass
in ThinLTO backend will run as usual looking up to external
symbol in the summary if needed.

Depends on D80985.

Reviewers: eugenis, pcc

Reviewed By: eugenis

Subscribers: inglorion, hiraditya, steven_wu, dexonsmith, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D81242