For llvm-objdump, add the option -private-header (without the trailing ’s’)

For llvm-objdump, add the option -private-header (without the trailing ’s’)
to only print the first private header.

Which for Mach-O files only prints the Mach header and not the subsequent load
commands.  Which is used by scripts to match what the darwin otool(1) with the
-h flag does without the -l flag.

For non-Mach-O files it has the same functionality as -private-headers (with
the trailing ’s’).

rdar://24158331

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257548 91177308-0d34-0410-b5e6-96231b3b80d8