Clear the cached cost when removing a function in

Clear the cached cost when removing a function in
the inliner; prevents nondeterministic behavior
when the same address is reallocated.
Don't build call graph nodes for debug intrinsic calls;
they're useless, and there were typically a lot of them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67311 91177308-0d34-0410-b5e6-96231b3b80d8