Fix .debug_frame dwarf unwinding through prelinked dynamic libraries.

Fix .debug_frame dwarf unwinding through prelinked dynamic libraries.

This wasn't immediately visible since often we would pick up the .eh_frame
CFI. But when the would pick up the CFI from the .debug_frame and the
shared library was prelinked, we would not correctly adjust some addresses.

* runtime/sym.h (_stp_module): Better explain dwarf_module_base.
* runtime/unwind.c (adjustStartLoc): Only adjust against dwarf_module_base
  when not eh_frame.
* translate.cxx (dump_unwindsyms): Adjust dwarf_module_base against dwbias.