This reverts commit f5bc7afe.

Such external debug info files are created by the dsymutil command.  Usually, it
creates a <name>.dSYM bundle directory but it can also produce a <name>.dwarf
flat file.  The code will find and use either.  It first checks if such a bundle
or file is adjacent to the module binary.  If it's not, it uses Spotlight to
search for a .dSYM bundle based on the binary's UUID, which is what gdb and lldb
do, too.  That way, it can find it anywhere on the system.

dbghelp: Don't parse the DWARF info from Mach-O files if we were requested to only provide public symbols.

This now works more like how the ELF and PE support works.

For backward compatibility with old, buggy GCC, Apple uses a different register
numbering scheme for the eh_frame section.

See, for reference, the comments near the top of this file from LLDB's source:
https://github.com/llvm-mirror/lldb/blob/release_36/source/Plugins/Process/Utility/RegisterContext_x86.h

From: Michael Müller <michael@fds-team.de>

Also lock/unlock the module only on creation/destruction of the object.

Also lock/unlock the module only on creation/destruction of the object.