abidw: Consolidate setting options

abidw: Consolidate setting options

When setting options meant to be used for the write_context, it is easy
to forget to change all relavant locations. In order to consolidate
that, introduce a set_opts function that sets various known options.

We benefit from earlier refactoring as now the write_context is passed
around to carry options for writers. Hence we can be sure, that if we
set up the context correctly (and do not use deprecated functionality),
the respective write_* function will see the options set in the context.

	* include/abg-writer.h (set_common_option): Declare new function.
	* tools/abidw.cc (load_corpus_and_write_abixml)
	(load_kernel_corpus_group_and_write_abixml): Use the newly
	introduced set_common_option.

Signed-off-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>