Fix DT_MIPS_RLD_MAP_REL tag for n64 target and 32-bit host.

Fix DT_MIPS_RLD_MAP_REL tag for n64 target and 32-bit host.

For the case of MIPS n64 target and 32-bit host, the computation of
the DT_MIPS_RLD_MAP_REL tag involves sdyn->output_section->vma +
sdyn->output_offset (64-bit) being added to b (32-bit host pointer),
so losing the high part and resulting in an incorrect
DT_MIPS_RLD_MAP_REL tag, and all dynamically linked glibc tests
failing for n64.  This patch fixes this (spot-tested with glibc tests;
however, I don't have a self-contained testcase for this bug).

	* elfxx-mips.c (_bfd_mips_elf_finish_dynamic_sections)
	<DT_MIPS_RLD_MAP_REL>: Add target address to host address
	difference, not to host pointer.