EPICS Base changed how it export cross compiled flags. Now we need to
check for "UNIX" and "linux".

This reverts commit 9b59288d.

Note that any module that depends on StreamDevice will load it first using `handleDependencies` which
is called before we add the _DB paths. So if a module depends on StreamDevice, this will be accurately
caught; moreover, if StreamDevice is not loaded, then we don't bother setting this path.