tools: adds and implements a --custom-targets command line switch

[0Grit]

Description

Per #6581

adds and implements a --custom-targets command line switch

If --custom-targets switch is provided, it will be used for custom_targets.json directory instead of the --source switch.

Was looking for a test of tools/options.py's extract_mcu's to update but didn't find.
Point me in the right direction if I missed it.

Pull request type

[ ] Fix
[ ] Refactor
[ ] Target update
[x] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

Reviewers

@theotherjimmy

[ciarmcom]

@loverdeg-ep, thank you for your changes.
@theotherjimmy @ARMmbed/mbed-os-tools @ARMmbed/mbed-os-maintainers please review.

[theotherjimmy]

Could you move the addition of --custom-targets into get_default_options_parser? Then you can remove it from get_config.py, make.py and test.py.

[theotherjimmy]

Was looking for a test of tools/options.py's extract_mcu's to update but didn't find.

I don't think we have a test for that. I'll accept any tests, and I can merge it with other tests if needed or if I find other tests later.

[0Grit]

Could you move the addition of --custom-targets into get_default_options_parser? Then you can remove it from get_config.py, make.py and test.py.

Was hoping you'd say that!

[theotherjimmy]

1 more duplicated addition of --custom-targets

[theotherjimmy]

Previously clicked the wrong radial button. Meant to request changes.

[0xc0170]

Can you also rebase, once you add commits to address review, thanks (will fix spellcheck failure)

[0Grit]

@theotherjimmy did I miss anything? any last requests?

[theotherjimmy]

@loverdeg-ep You missed nothing.

[0xc0170]

Ci started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts