PR22829, objcopy/strip removes PT_GNU_RELRO from lld binaries

PR22829, objcopy/strip removes PT_GNU_RELRO from lld binaries

lld lays out the relro segment differently to GNU ld, not bothering to
include the first few bytes of .got.plt and padding out to a page at
the end of the segment.  This patch teaches binutils to recognize the
different (and somewhat inferior) layout as valid.

bfd/
	PR 22829
	* elf.c (assign_file_positions_for_non_load_sections): Rewrite
	PT_GNU_RELRO setup.
ld/
	* testsuite/ld-x86-64/pr14207.d: Adjust relro p_filesz.