Change frame_filter_flags to use DEF_ENUM_FLAGS_TYPE

This changes frame_filter_flags to use DEF_ENUM_FLAGS_TYPE, and
updates all the uses.  It also changes the enum constants to use <<,
as suggested by Sergio.

ChangeLog
2018-02-26  Tom Tromey  <tom@tromey.com>

	* stack.c (backtrace_command_1): Update.
	* python/python-internal.h (gdbpy_apply_frame_filter): Change type
	of "flags".
	* python/py-framefilter.c (py_print_frame)
	(gdbpy_apply_frame_filter): Change type of "flags".
	* mi/mi-cmd-stack.c (mi_apply_ext_lang_frame_filter): Change type
	of "flags".
	(mi_cmd_stack_list_frames, mi_cmd_stack_list_locals)
	(mi_cmd_stack_list_args, mi_cmd_stack_list_variables): Update.
	* extension.h (enum frame_filter_flag): Rename from
	frame_filter_flags.
	(frame_filter_flags): Define using DEF_ENUM_FLAGS_TYPE.
	(apply_ext_lang_frame_filter): Change type of "flags".
	* extension.c (apply_ext_lang_frame_filter): Change type of
	"flags".
	* extension-priv.h (struct extension_language_ops)
	<apply_frame_filter>: Change type of "flags".