* som.h (struct som_exec_data): New structure to hold exec

	* som.h (struct som_exec_data): New structure to hold exec
	info that must be preserved when running objcopy/strip.
	(struct somdata): Add new "exec_data" field and accessor
	macro.  Add some comments on how the various fields are used.
	(som_section_data_struct): Make is_space and is_subspace bitfields.
	Delete unused subspace_index.  All references now use the
	target_index field within the section structure itself.

	* som.c (make_unique_section): Delete unused declaration.
	(som_bfd_copy_private_bfd_data): New function.
	(som_object_setup): Allocate space for and save exec information
	that needs to be copied during objcopy/strip.
	(som_mkobject): Do not allocate space for a file header here.
	It is not used when only reading SOM objects.
	(som_prep_headers): Allocate space for and attach a file header
	to the output bfd.  For executables, use the saved system_id
	value rather than trying to guess the right value.  Do not abort
	wwhen setting file_hdr->entry* for executables.
	(som_begin_writing): For executables, set the exec_entry and
	exec_flags fields.
	(som_copy_private_backend_section_data): Always return a value.