Fix --defsym to copy symbol attributes.

Fix --defsym to copy symbol attributes.

Alan Modra committed a patch to Gnu ld to fix a problem encountered on
PPC where the --defsym option wasn't copying the st_other bits to the
newly-defined symbol.

    https://sourceware.org/ml/binutils/2014-07/msg00094.html

Gold has the same problem, and additionally wasn't copying the symbol type.
This patch fixes both problems, by copying the symbol type, visibility, and
the remaining st_other bits to the new symbol for --defsym=sym1=sym2
assignments.

gold/
	* expression.cc (struct Expression::Expression_eval_info): Add
	new fields type_pointer, vis_pointer, and nonvis_pointer.
	(Expression::eval_maybe_dot): Add type_pointer, vis_pointer, and
	nonvis_pointer parameters. Adjust all calls.
	(Symbol_expression::value): Update type, visibility, and nonvis bits
	in caller.
	* script.cc (Symbol_assignment::sized_finalize): Update type,
	visibility, and remaining st_other bits for new symbol.
	* script.h: (Expression::eval_maybe_dot): Add type_pointer,
	vis_pointer, and nonvis_pointer parameters.
	* symtab.h (Symbol::set_type): New method.

	* testsuite/Makefile.am (defsym_test): New test.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/defsym_test.c: New file.
	* testsuite/defsym_test.sh: New file.