MacOS "debugging symbols" don't actually include any DWARF

Mach-O leaves debugging information in the .o files, and the "debug info" in the actual binary is just a debug map that tells the debugger which .o file to look in. A .dSYM can be created which embeds all this information by using `dsymutil`, but we're currently not doing that, so the debuginfo provided for MacOS is mostly useless.