LTO: get_section: add new argument

LTO: get_section: add new argument

gcc/ChangeLog:

	PR lto/97508
	* langhooks.c (lhd_begin_section): Call get_section with
	not_existing = true.
	* output.h (get_section): Add new argument.
	* varasm.c (get_section): Fail when NOT_EXISTING is true
	and a section already exists.
	* ipa-cp.c (ipcp_write_summary): Remove.
	(ipcp_read_summary): Likewise.
	* ipa-fnsummary.c (ipa_fn_summary_read): Always read jump
	functions summary.
	(ipa_fn_summary_write): Always stream it.