ld: Add "-z separate-code" option to ELF linker

ld: Add "-z separate-code" option to ELF linker

The new "-z separate-code" option will generate separate code LOAD
segment which must be in wholly disjoint pages from any other data.

include/

	PR ld/22393
	* bfdlink.h (bfd_link_info): Add separate_code.

ld/

	PR ld/22393
	* NEWS: Mention "-z separate-code".
	* emultempl/elf32.em (gld${EMULATION_NAME}_get_script): Get
	builtin linker scripts and return linker scripts from disk for
	"-z separate-code".
	(gld${EMULATION_NAME}_handle_option): Handle "-z separate-code"
	and "-z noseparate-code".
	* genscripts.sh: Generate linker scripts for "-z separate-code".
	(LD_FLAG): Set to *textonly for "-z separate-code".
	* ld.texinfo: Document "-z separate-code".
	* lexsup.c (elf_shlib_list_options): Add linker help messsages
	for "-z separate-code" and "-z noseparate-code".
	* scripttempl/elf.sc (SEPARATE_TEXT): New
	(TEXT_SEGMENT_ALIGN): Likewise.
	Use ${TEXT_SEGMENT_ALIGN} to align and pad text segment to
	${MAXPAGESIZE}.