StackProtector: ensure stack checks are inserted before the tail call

The IR stack protector pass should insert stack checks before the tail
calls not only the musttail calls. So that the attributes `ssqreq` and
`tail call`, which are emited by llvm-opt, could be both enabled by
llvm-llc.

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D133860