Fix Windows/SPU/NTO/Lynx gdbserver builds

Fix Windows/SPU/NTO/Lynx gdbserver builds

I forgot to update these target_ops instances when I added these new
hooks.

I confirmed mingw32-w64 builds again at least.

gdb/gdbserver/ChangeLog:
2015-03-05  Pedro Alves  <palves@redhat.com>

	* lynx-low.c (lynx_target_ops): Install NULL hooks for
	stopped_by_sw_breakpoint, supports_stopped_by_sw_breakpoint,
	stopped_by_hw_breakpoint, supports_stopped_by_hw_breakpoint.
	* nto-low.c (nto_target_ops): Likewise.
	* spu-low.c (spu_target_ops): Likewise.
	* win32-low.c (win32_target_ops): Likewise.