Revert "Reland "[pgo] Avoid introducing relocations by using private alias""

This caused lld on mac to assert when building instrumented clang (or
instrumented code in general). See comment on the code review for
reproducer.

> In many cases, we can use an alias to avoid a symbolic relocations,
> instead of using the public, interposable symbol. When the instrumented
> function is in a COMDAT, we can use a hidden alias, and still avoid
> references to discarded sections.
>
> New compiler-rt tests are Linux only for now.
>
> Previous versions of this patch allowed the compiler to name the
> generated alias, but that would only be valid when the functions were
> local. Since the alias may be used across TUs we use a more
> deterministic naming convention, and add a `.local` suffix to the alias
> name just as we do for relative vtables aliases.
>
> Reviewed By: phosek
>
> Differential Revision: https://reviews.llvm.org/D137982

This reverts commit c42e50fe.