Fix sigtramp frame handlers to use THIS frame and be endian friendly.

2013-03-05  Jeremy Bennett <jeremy.bennett@embecosm.com>

	* arc-linux-tdep.c (SIGTRAMP_INSNS_LENGTH): Deleted.
	(arc_sigtramp_insns): Moved into arc_linux_is_sigtramp.
	(arc_linux_is_sigtramp): Define arc_sigtramp_insns locally,
	replace SIGTRAMP_INSNS_LENGTH with sizeof. Make endian friendly.
	(arc_linux_sigcontext_addr): Use THIS frame.