hurd: Avoid PLTs for __mach_thread_self and __mach_reply_port

	* mach/mach/mach_traps.h (__mach_reply_port, __mach_thread_self,
	__mach_task_self, __mach_host_self, __swtch, __swtch_pri,
	__thread_switch, __evc_wait): Move declarations to...
	* sysdeps/mach/include/mach/mach_traps.h: ... new file, and add
	attribute_hidden.