This test covers the case where the resource script references a file which
is created by a custom_target (in this case, an icon).
Put icon in a separate directory to ensure we excercise setting the include
path to the directory which contains it.
In this case, the arguments to MinGW windres will contain spaces and
the test will definitely fail, so just skip it.
This effectively means that manually running the test will be fine, but
running it via run_project_tests.py will always fail (skip).