PR 10450

	PR 10450
	* output.h (class Output_section): Add is_entsize_zero_ field.
	* output.cc (Output_section::Output_section): Initialize
	is_entsize_zero_.
	(Output_section::set_entsize): If two different entsizes are
	requested, force it to zero.
	(Output_section::add_input_section): Set flags for .debug_str
	before updating section flags.  Set entsize.
	(Output_section::update_flags_for_input_section): Set SHF_MERGE
	and SHF_STRING if all input sections have those flags.