PT_LOAD and PT_GNU_RELRO segment overlap

PT_LOAD and PT_GNU_RELRO segment overlap

Commit 325ba6fb34 excluded degenerate zero length PT_LOAD segments,
but that only fixed part of the problem, which was that the load
segment limits were not calculated properly.

	PR 22845
	* elf.c (IS_TBSS): Define.
	(_bfd_elf_map_sections_to_segments): Use IS_TBSS.
	(assign_file_positions_for_non_load_sections): Revert last change.
	Properly calculate load segment limits to compare against relro limits.