[BOLT] Reintroduce allow-stripped

Reject stripped binaries as a policy.

The core issue with stripped binaries is that we can't detect the presence
of split functions which require extra handling. Therefore BOLT can't ensure
functional correctness of produced binary if the input stripped binary contains
split functions. Supporting such cases is an interesting problem but it goes
against BOLT's intended goal of achieving peak program performance.

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D142686