Fix SHF_GNU_RETAIN testsuite fallout

Fix SHF_GNU_RETAIN testsuite fallout

binutils/ChangeLog:

	* testsuite/binutils-all/readelf-maskos-1a.d: Fix test for unrecognized
	bit set in SHF_MASKOS range.
	* testsuite/binutils-all/readelf-maskos-1b.d: Likewise.
	* testsuite/binutils-all/readelf-maskos-unknown.s: New test.

ld/ChangeLog:

	* testsuite/ld-elf/retain3.s: Move symbolic reference into writeable
	.data section from read-only .text section.
	* testsuite/ld-elf/retain5.d: Don't pass --print-gc-sections for test
	that doesn't require it.
	* testsuite/ld-elf/retain6a.d: Adjust test.
	* testsuite/ld-elf/retain6main.s: Move symbolic reference into writeable
	.data section from read-only .text section.