Revert revisions 28791, 28794 and 28795. AB_PRIVATE_EXTERN is only available for Mach-o

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28836 3ad0048d-3df7-0310-abae-a5850022a9f2
+ add a new unit which will contain basic functions related to handling packages

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28837 3ad0048d-3df7-0310-abae-a5850022a9f2