Fortran: check for undeclared variables by forcing implicit none everywhere
C/C++: check for unused parameters and return types
removed unused variables from test cases
ci: do missing return and unused arg check with Github Actions
In this test, we try to manually link against the generated library to
create an executable and then run it to verify that it works.
Also test for all possible library versioning in the versioning tests on
Windows. Even though they yield the same dll naming, we should still
test it.
Alex Băluț reported that on OS X libfoo.0.dylib cannot be found as -lfoo by the
linker, and you must use -lfoo.0 instead. Add a test for this so the CI can
catch such problems. The next commit will contain the fix.