[llvm-objdump] Align instructions to a tab stop in disassembly output

This relands D60376/rL358405, with the difference: sed 'y/\t/ /' -> tr '\t' ' '
BSD sed doesn't support escape characters for the 'y' command.
I didn't use it in rL358405 because it was not listed at
https://llvm.org/docs/GettingStarted.html#software but it
should be available.

Original description:

In GNU objdump, -w/--wide aligns instructions in the disassembly output.
This patch does the same to llvm-objdump. However, we always use the
wide format (-w/--wide is ignored), because the narrow format
(instructions are misaligned) is probably not very useful.

In llvm-readobj, we made a similar decision: always use the wide format,
accept but ignore -W/--wide.

To save some columns, we change the tab before hex bytes (controlled by
--[no-]show-raw-insn) to a space.

llvm-svn: 358474