Not only are `Step.Compile` methods like `linkLibC()` redundant because
`Module` exposes the same APIs, it also might not be immediately obvious
to users that these methods modify the underlying root module, which can
be a footgun and lead to unintended results if the module is exported to
package consumers or shared by multiple compile steps.

Using `compile.root_module.link_libc = true` makes it more clear to
users which of the compile step and the module owns which options.