fcm make: inherited build: fix non-failure

Recipe to repeat bug:
* Inherit a build.
* Override with 2 independent Fortran source files containing modules.
* Both files cause build failure. (E.g. due to syntax error.)
* Run fcm make once, 1st source file fails.
* Fix 1st source file.
* Run fcm make again. Should fail, but doesn't.

This change fixes the problem.
Merge pull request #111 from matthewrmshin/fix-build-2-bad-mod-over-inherit

fcm make: inherited build: fix non-failure