LTO and optional features

[scj643]

Changes to make LTO work as well as working with MOUSEKEY_ENABLE = false

Description

Changes that allow LTO to compile and make option features actually optional.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[scj643]

@lokher thoughts on this?

[scj643]

This will close #420