gdb: Fix ia64 defining TRAP_HWBKPT before including gdb_wait.h

gdb: Fix ia64 defining TRAP_HWBKPT before including gdb_wait.h

On ia64, gdb_wait.h eventually includes siginfo-consts-arch.h, which
contains an enum with TRAP_HWBKPT, along with a #define. Thus we cannot
define TRAP_HWBKPT to 4 beforehand, and so gdb_wait.h must be included
earlier; include it from linux-ptrace.h so it can never come afterwards.

gdb/ChangeLog:

	* nat/linux-ptrace.c: Remove unnecessary reinclusion of
	gdb_ptrace.h, and move including gdb_wait.h ...
	* nat/linux-ptrace.h: ... to here.