[llvm] [llvm-objdump] Add triple support to `mcpu=help` (PR #165661)

[Ruoyu Qiu via llvm-commits]

cabbaken wrote:

I propose updating the test cases to follow this structure:
>--mcpu=help + --disassemble + objects specified + other dump options, no --triple:
a. mcpu help should be printed for the targets specified (as current behaviour).
b. Disassembly should be printed for specified objects (as current behaviour).
c. Other dump options should be printed for specified objects.
--mcpu=help + --disassemble + no objects specified + other dump options, no --triple
a. Same as 1. but with a.out treated as the object, if it exists.
b. If a.out doesn't exist, we want some form of error, because we don't know which target to dump the mcpu help text for.
--mcpu=help + --disassemble + no objects specified + other dump options, --triple
a. As 2. but target derived from --triple option value.
b. If a.out doesn't exist, print MCPU help derived from --triple and don't emit an error.
--mcpu=help + no --disassemble
a. Same as above cases, depending on other option values (--disassemble is not required to print MCPU help text).
b. If no other dump options specified, exit success and no errors.

Would this be clearer?

https://github.com/llvm/llvm-project/pull/165661