If -fomit-frame-pointer is used, we still need to record when the %esp register

If -fomit-frame-pointer is used, we still need to record when the %esp register
is modified. Otherwise, the unwinder will get confused. The old code (before I
started my hacking) did this. It dropped on the floor, because I wasn't aware of
this requirement.

On the plus side, if we use "alloca" in a function, we create frame pointers
even with -fomit-frame-pointer is enabled!

This is a Good Thing(tm)!!!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75183 91177308-0d34-0410-b5e6-96231b3b80d8