Some of these options are designed to be a no-op when used on a Spec
that doesn't match the platform for the option. However, if the given
plaform was not present, they would panic.
This patch:
- Adds an early-return for options that are only applied on a
specific platform.
- Update the GoDoc for these functions to describe they're a
no-op on other platforms.
- Adds some rudimentary unit-tests to verify their behavior.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>