Introduce -polly-process-unprofitable

This single option replaces -polly-detect-unprofitable and -polly-no-early-exit
and is supposed to be the only option that disables compile-time heuristics that
aim to bail out early on scops that are believed to not benefit from Polly
optimizations.

Suggested-by:  Johannes Doerfert
llvm-svn: 249426