LD: Export relative-from-absolute symbol marking to BFD

LD: Export relative-from-absolute symbol marking to BFD

It is usually possible to tell absolute and ordinary symbols apart in
BFD throughout the link, by checking whether the section that owns the
symbol is absolute or not.

That however does not work for ordinary symbols defined in a linker
script outside an output section statement.  Initially such symbols are
entered into to the link hash as absolute symbols, owned by the absolute
section.  A flag is set in the internal linker expression defining such
symbols to tell the linker to convert them to section-relative ones in
the final phase of the link.  That flag is however not accessible to BFD
linker code, including BFD target code in particular.

Add a flag to the link hash then to copy the information held in the
linker expression.  Define a macro, `bfd_is_abs_symbol', for BFD code to
use where determining whether a symbol is absolute or ordinary is
required before the final link phase.

This macro will correctly identify the special `__ehdr_start' symbol as
ordinary throughout link, for example, even though early on it will be
assigned to the absolute section.  Of course this does not let BFD code
identify what the symbol's ultimate section will be before the final
link phase has converted this symbol (in `update_definedness').

	include/
	* bfdlink.h (bfd_link_hash_entry): Add `rel_from_abs' member.

	bfd/
	* linker.c (bfd_is_abs_symbol): New macro.
	* bfd-in2.h: Regenerate.

	ld/
	* ldexp.c (exp_fold_tree_1) <etree_assign, etree_provide>
	<etree_provided>: Copy expression's `rel_from_abs' flag to the
	link hash.