Add a new target flag which determines whether the target supports dynamic packages or not.

systems.pas:
  + new flag tf_supports_packages
pmodules.pas, proc_package:
  * error out when flag tf_supports_packages is not set for the current target
msg/errore.msg:
  + error message for when tf_supports_packages is missing and a package file is compiled

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28237 3ad0048d-3df7-0310-abae-a5850022a9f2