In Mac dump_syms, allow reading debug data out of both the Mach-O file and the dSYM.

This adds a new |-g <dSYM path>| flag to dump_syms, to specify the dSYM path for
the target Mach-O argument. The UUIDs and architectures of the two paths must
match in order to dump symbols for this "split module."

This reason for this is that for x86_64 binaries on OS X, the CFI data is stored
in the __TEXT,__eh_frame segment of the Mach-O file, and the data is not copied
into the dSYM by dsymutil.  Therefore, just dumping the dSYM doesn't yield CFI
data for x86_64 files, and both the dSYM and the Mach-O file must be dumped in
order to produce a complete Breakpad symbol file. For i386 binaries, the CFI data
is stored in the __DWARF,__debug_frame segment, which is part of the dSYM, so
this isn't necessary.

BUG=https://code.google.com/p/chromium/issues/detail?id=393594
R=mark@chromium.org

Review URL: https://breakpad.appspot.com/6704002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1359 4c0a9323-5329-0410-9bdc-e9ce6186880e