Fix misplacement of a relaxed section on AArch64.

Fix misplacement of a relaxed section on AArch64.

gold/ChangeLog
	PR gold/21430
	* aarch64.cc
	(AArch64_relobj::convert_input_section_to_relaxed_section):
	Set the section offset to -1ULL.
	(Target_aarch64::relocate_section): Adjust the view in case
	of a relaxed input section.
	* testsuite/Makefile.am (pr21430): New test.
	* testsuite/Makefile.in: Regenerate
	* testsuite/pr21430.s: New test source file.
	* testsuite/pr21430.sh: New test script.