bfd: Improve lookup of file / line information for errors

bfd: Improve lookup of file / line information for errors

When looking up file and line information (used from the linker to
report error messages) if no symbol is passed in, then use the symbol
list to look for a matching symbol.

If a matching symbol is found then use this to look up the file / line
information.

This should improve errors when looking up file / line information for
data sections.  Hopefully we should find a matching data symbol, which
should, in turn (we hope) match a DW_TAG_variable in the DWARF, this
should allow us to give accurate file / line errors for data symbols.

As the hope is to find a matching DW_TAG_variable in the DWARF then we
ignore section symbols, and prefer global symbols to locals.

bfd/ChangeLog:

	* dwarf2.c (_bfd_dwarf2_find_nearest_line): Perform symbol lookup
	before trying to fine matching file and line information.

ld/ChangeLog:

	* testsuite/ld-elf/shared.exp: Update expected results.
	* testsuite/ld-elf/dwarf2.err: Likewise