This PR introduces the possibility of using multiple commands for thec.combine pattern, and infrastructure that will enable using the same logic on any build step, if so decided.

Two changes in behavior are introduced:

• When looking for multi-step recipes (e.g. hooks) inRunRecipe(), a key that exactly matchesprefix.suffix is explicitly ignored if numbered entries are found, and only used as a fallback when no other entries are present.
  This change is consistent with current docs that require aprefix.NNN.suffix syntax for multi-step recipes. A property namedprefix.suffix is undefined behavior, and is currently included among the numbered ones.

• Reuse theRunRecipe logic for therecipe.c.combine step to allow multi-stage linking. The above change in this context means that numbered steps have priority over the single property, but both can be specified to maintain backwards compatibility (the new numbered properties are ignored by the current IDE).

NO TESTS as I don't know where to add the test case... 😇 BUT I tried with a core that defined these rules and got the exact behavior I described here. If someone can give me pointers I can add the proper test case.

Feel free to cherry-pick and/or edit and/or shoot down at will 😅