* system.h (const, inline): Move the stage2 handling of these
        keywords-as-macros from here...
        * gansidecl.h (const, inline): ...to here.
(This became necessary after using `const' in config directory headers,
which get included before system.h does.  If we're going to reset these
keywords, we must do so before absolutely any other header file.)

From-SVN: r25626