* system.h: Use putc_unlocked, fputc_unlocked, and
        fputs_unlocked only if putc_unlocked has a prototype already.
        Prototype fputs_unlocked if necessary.
        * configure.in: Check for prototypes of putc_unlocked and
        fputs_unlocked.
        * acconfig.h: Updated.
        * config.in, configure: Rebuilt.

From-SVN: r25855