This directory contains the interface code between the Modula-2 front
end and GCC.  In effect this is the Modula-2 compiler GCC Tree API.
It is an internal API only.  Many of these filenames match their GCC C
family counterparts.  So for example m2decl.def and m2decl.cc are the
Modula-2 front end version of c-decl.cc.