Crucial C++ inlining broken under -Os

[Joern Rennecke]

Quoting Richard Guenther <richard.guenther@gmail.com>:

> That is, we no longer optimistically assume that comdat functions
> can be eliminated if there are no callers in the local TU in 4.5
> (but we did in previous releases).

But if the function is very simple, the only reason to keep it would be
if its address was taken somewhere, or if we tailcall it.