(PUP-2912) PMT Build symlink exception

Prior to this commit the build command would add symlinks to packages. This
can cause unexpected behavior when installed on a system.
This commit causes the build command to throw an error when it finds a symlink.
That should prevent new modules from being created with a symlink included.
The warnings from this should probably indicate which module they came from, and would ideally reflect the module's final destination (neither of which can be known inside this class).