Since it can be set in the environment when running the test suite,
guard tests which are sensitive to intermediate directory strategy
changes with explicit settings.
Sources that are part of a unity build are normally not compiled
individually. However, the VS IDE allows a single source to be
compiled. This can also be achieved on the command line:
msbuild my.vcxproj ... -t:ClCompile -p:SelectedFiles=<src>
where `<src>` is the path in the vcxproj `ClCompile` entry.
In a target with precompiled headers, the source needs PCH settings to
support individual compilation even if the normal unity build does not.
Ben Boeckel