Fix problem where script specified both address and region for a section.

Fix problem where script specified both address and region for a section.

If a script specifies both address and region for an output section
declaration, gold ignores the region specification. This can lead to
bogus "moves backward" errors. This patch fixes gold so that if a
section specifies both address and region, it will place the section
at the specified address in the region, and update the location counter
within the region.

gold/
	PR gold/18847
	* script-sections.cc (Memory_region::set_address): New method.
	(Script_sections::find_memory_region): Add explicit_only parameter.
	(Output_section_definition::set_section_addresses): Handle case where
	script specifies both address and vma region.
	* script-sections.h (Script_sections::find_memory_region): Add
	explicit_only parameter.