This teaches the 'testing' test to try generator expressions in
arguments to add_test(NAME). This test case mimics a common use-case of
passing executables to test driver scripts. We excercise the syntax for
per-configuration target file names.
This creates command mode add_test(NAME ...). This signature is
extensible with more keyword arguments later. The main purpose is to
enable automatic replacement of target names with built target file
locations. A side effect of this feature is support for tests that only
run under specific configurations.
The 'testing' CMake test builds a project that uses add_test. This
strengthens the test to actually run CTest on the project build tree
after building it.
