Sort inherited products correctly

We pass the filename without the extension to
rblf.inherit(). Removing the extension changes the
sort order when one file's name is a prefix of another:

```
>>> sorted(["base", "base-secondary"])
['base', 'base-secondary']
>>> sorted(["base.mk", "base-secondary.mk"])
['base-secondary.mk', 'base.mk']
```

Correct the sort order so that global variables get
their correct ordering.

Bug: 229132189
Test: ./out/rbcrun ./build/make/tests/run.rbc
Change-Id: I22367eb49b33956b71ac1b966fe78c1308b94257