Relevant BUGIDs: 643357

Relevant BUGIDs: 643357

Purpose of commit: bugfix

Commit summary:
---------------
Patch from Sam Hartman to fix handling of module linking on Linux:
modules should be linked against libpam if they call any functions from
the library, since not all platforms will correctly resolve symbol
references otherwise.  Also, make sure we use gcc, not ld, when linking,
since there's additional linker glue that gcc will pull in for us.