Added a "platforms" target which lists the available platforms.  Previously this information was presented by the help target at all times, however as a consequence of Andrew's changes, it became infeasible to present this information once the makefiles were already configured.  The platforms target works around this limitation by performing the extra work needed to list the platforms only if explicitly requested by the user.
Added a "platforms" target which lists the available platforms.  Previously
this information was presented by the help target at all times, however as
a consequence of Andrew's changes, it became infeasible to present this
information once the makefiles were already configured.  The platforms
target works around this limitation by performing the extra work needed
to list the platforms only if explicitly requested by the user.


git-svn-id: 28d9401aa571d5108e51b194aae6f24ca5964c06@1099 8cc4aa7f-3514-0410-904f-f2cc9021211c

crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS