This is similar to D83530, but for llvm-objdump.
The motivation is the desire to add an `llvm-otool` symlink to
llvm-objdump that behaves like macOS's `otool`, using the same
technique the at llvm-objcopy uses to behave like `strip` (etc).
This change for the most part preserves behavior. In some cases,
it increases compatibility with GNU objdump a bit. For example,
the long options now require two dashes, and the long options
taking arguments for the most part now require a `=` in front
of the value. Exceptions are flags where tests passed the
value separately, for these the separate form is kept as
an alias to the = form.
The one-letter short form args are now joined or separate
and long longer accept a =, which also matches GNU objdump.
cl::opt<>s in libraries now have to be explicitly plumbed
through. This patch does that for --x86-asm-syntax=, but
there's hope that we can remove that again.
Differential Revision: https://reviews.llvm.org/D100433
