Fix some bugs in the posix output of llvm-nm. Which is documented on

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/nm.html .

1) For Mach-O files the code was not printing the values in hex as is the default.
2) The values printed had leading zeros which they should not have.
3) The address for undefined symbols was printed as spaces instead of 0.
4) With the -A option with posix output for an archive did not use square
brackets around the archive member name.

rdar://25311883 and rdar://25299678

llvm-svn: 264778