Fix inheritance order

The children to inherit from were not sorted. This
wasn't a problem for list variables, because all those
inheritances get merged together based on the @inherit/
values in the list variables. But for single value variables
it made a difference.

Bug: 226206409
Test: ./out/rbcrun ./build/make/tests/run.rbc
Change-Id: Ib56bbb91a79fe8c7cb780c253f5bd8d6c0e87765