swift234

CMake: fix a bug where only_validation-only_non_executable test configuration was running all tests

A nested loop was adding arguments specific to the current iteration to
a variable, where the arguments persisted into the next iteration.

The issue only affected the only_validation-only_non_executable
configuration, here's why.  The test subsets were configured in the
following order: primary, validation, all, only_validation, only_long.
The first three were not adding new arguments.  'all' was adding
arguments that were affecting 'only_validation'.  Then 'only_long' was
adding an argument of its own that was overriding the argument from
'all'.