RISC-V: Generalize -march support, add ELF attribute support.

RISC-V: Generalize -march support, add ELF attribute support.

	Kito Cheng  <kito.cheng@gmail.com>
	Monk Chiang  <sh.chiang04@gmail.com>

	gcc/
	* common/config/riscv/riscv-common.c: Include sstream.
	(riscv_subset_list::to_string): New.
	(riscv_arch_str): Likewise.
	* config.gcc (riscv*-*-*): Handle --with-riscv-attribute=
	* config.in: Regen.
	* config/riscv/riscv-protos.h (riscv_arch_str): New.
	* config/riscv/riscv.c (INCLUDE_STRING): Defined.
	(riscv_emit_attribute): New.
	(riscv_file_start): Emit attribute if needed.
	(riscv_option_override): Init riscv_emit_attribute_p.
	* config/riscv/riscv.opt (mriscv-attribute): New option.
	* configure.ac (riscv*-*-*): Check binutils is supporting ELF
	* configure: Regen.
	* doc/install.texi: Document --with-riscv-attribute.
	* doc/invoke.texi: Document -mriscv-attribute.

	* common/config/riscv/riscv-common.c:
	Include config/riscv/riscv-protos.h.
	(INCLUDE_STRING): Defined.
	(RISCV_DONT_CARE_VERSION): Defined.
	(riscv_subset_t): Declare.
	(riscv_subset_t::riscv_subset_t): New.
	(riscv_subset_list): Declare.
	(riscv_subset_list::riscv_subset_list): New.
	(riscv_subset_list::~riscv_subset_list): Likewise.
	(riscv_subset_list::parsing_subset_version): Likewise.
	(riscv_subset_list::parse_std_ext): Likewise.
	(riscv_subset_list::parse_sv_or_non_std_ext): Likewise.
	(riscv_subset_list::add): Likewise.
	(riscv_subset_list::lookup): Likewise.
	(riscv_subset_list::xlen): Likewise.
	(riscv_subset_list::parse): Likewise.
	(riscv_supported_std_ext): Likewise.
	(current_subset_list): Likewise.
	(riscv_parse_arch_string): Using riscv_subset_list::parse to
	parse.

	gcc/testsuite/
	* gcc.target/riscv/attribute-1.c: New.
	* gcc.target/riscv/attribute-2.c: Likewise.
	* gcc.target/riscv/attribute-3.c: Likewise.
	* gcc.target/riscv/attribute-4.c: Likewise.
	* gcc.target/riscv/attribute-5.c: Likewise.
	* gcc.target/riscv/attribute-6.c: Likewise.
	* gcc.target/riscv/attribute-7.c: Likewise.
	* gcc.target/riscv/attribute-8.c: Likewise.
	* gcc.target/riscv/attribute-9.c: Likewise.

	* gcc.target/riscv/arch-1.c: New.
	* gcc.target/riscv/arch-2.c: Likewise.
	* gcc.target/riscv/arch-3.c: Likewise.
	* gcc.target/riscv/arch-4.c: Likewise.

Co-Authored-By: Monk Chiang <sh.chiang04@gmail.com>
From-SVN: r269337