objdump: Don't print a (always 0) size for MachO symbols.

Only common symbol on MachO and COFF have a size.

For COFF we already had a custom format.

For MachO, there is no native objdump and we were printing it as ELF. Now
we only print the sizes for symbols that actually have them.

llvm-svn: 240422
3 files changed