Fix -Wmissing-prototypes build warnings on Darwin.

Fix -Wmissing-prototypes build warnings on Darwin.

gdb/
2012-03-13  Josh Matthews  <josh@joshmatthews.net>

	* darwin-nat-info.c (_initialize_darwin_info_commands): Add
	prototype.
	(darwin_debug_port_info): Make static.
	* darwin-nat.c (_initialize_darwin_inferior): Add prototype.
	* machoread.c (_initialize_machoread): Add prototype.
	* i386-darwin-nat.c (i386_darwin_dr_set, i386_darwin_dr_get)
	(i386_darwin_set_control, i386_darwin_get_control)
	i386_darwin_dr_set_addr, i386_darwin_get_addr)
	i386_darwin_get_status, i386_darwin_get_control):
	Comment out with HW_WATCHPOINT_NOT_YET_ENABLED macro.