PR47785: Add support for handling Xassembler/Wa options with LTO.

PR47785: Add support for handling Xassembler/Wa options with LTO.

2020-02-24  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
	    Kugan Vivekandarajah  <kugan.vivekanandarajah@linaro.org>

	PR driver/47785
	* gcc.c (putenv_COLLECT_AS_OPTIONS): New function.
	(driver::main): Call putenv_COLLECT_AS_OPTIONS.
	* opts-common.c (parse_options_from_collect_gcc_options): New function.
	(prepend_xassembler_to_collect_as_options): Likewise.
	* opts.h (parse_options_from_collect_gcc_options): Declare prototype.
	(prepend_xassembler_to_collect_as_options): Likewise.
	* lto-opts.c (lto_write_options): Stream assembler options
	in COLLECT_AS_OPTIONS.
	* lto-wrapper.c (xassembler_options_error): New static variable.
	(get_options_from_collect_gcc_options): Move parsing options code to
	parse_options_from_collect_gcc_options and call it.
	(merge_and_complain): Validate -Xassembler options.
	(append_compiler_options): Handle OPT_Xassembler.
	(run_gcc): Append command line -Xassembler options to
	collect_gcc_options.
	* doc/invoke.texi: Add documentation about using Xassembler
	options with LTO.

testsuite/
	* gcc.target/arm/pr78353-1.c: New test.
	* gcc.target/arm/pr78353-2.c: Likewise.