Convert function definitions and declarations to standard C.

Convert function definitions and declarations to standard C.
* src/vm-limit.c (memory_warnings):
* src/keyboard.c (modify_event_symbol):
* src/floatfns.c (rounding_driver, ceiling2, floor2, truncate2)
(round2, emacs_rint):
* src/process.c (send_process, old_sigpipe): Convert function
definitions and declarations to standard C.