From outside of macho_module.c, it's only called with NULL.  When it's
called with a non-NULL parameter, it's just a thin wrapper around
macho_load_debug_info_from_map(), so the code can just call that
directly.

OS X uses a struct nlist_64 for 64-bit images, where the n_value field is a
64-bit unsigned integer.

This matches more recent versions of Windows.

NT-style paths that have a device prefix (\??\) also return the drive
of the current working directory (even if they're valid devices).

Paths that are not NT and not even close to DOS don't actually fail
catastrophically.  Even though MSDN suggests that it returns the boot
drive in this case, tests indicate that it returns the drive of the
current working directory.

Add support for "semi-DOS" paths, these paths revert to the drive
letter specified in the first character.

The purpose of this function is to return the most fundamental path
without leaving a filesystem.  Steam uses this so that it can use inode
searches, without this functionality some installations/validations will
fail if the Steam Library is not on the same drive as Steam
itself (symlink'd to another location).