Advanced guessing of rendezvous breakpoint (resubmit)

When rendezvous structure is not initialized we need to set up
rendezvous breakpoint anyway. In this case the code will locate
dynamic loader (interpreter) and look for known function names.

This is r322209, but with fixed VDSO loading fixed.

Bug: https://bugs.llvm.org/show_bug.cgi?id=25806
Differential Revision: https://reviews.llvm.org/D41533

llvm-svn: 322251