* libc/include/_ansi.h: Add new _EXFNPTR macro for using with
function pointer arguments.
* libc/iconv/lib/conv.h: Use _EXFNPTR rather than _EXPARM macro.
* libc/iconv/lib/ucsconv.h: Ditto.
* libc/include/stdlib.h: Use new _EXFNPTR macro for function pointers.
* libc/include/sys/reent.h: Ditto.
* libc/include/sys/unistd.h: Ditto.
* libc/search/bsearch.c: Ditto.
* libc/stdio/fseek.c: Ditto.
* libc/stdio64/fseeko64.c: Ditto.
* libc/stdlib/atexit.c: Ditto.
* libc/stdlib/on_exit.c: Ditto.
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