[NDS32] Support Linux target for nds32.

[NDS32] Support Linux target for nds32.

gcc/
	* config.gcc (nds32*): Use nds32-linux.opt and nds32-elf.opt.
	(nds32le-*-*, nds32be-*-*): Integrate checking process.
	(nds32*-*-*): Add glibc and uclibc conditions.
	* common/config/nds32/nds32-common.c (nds32_except_unwind_info): New.
	(TARGET_EXCEPT_UNWIND_INFO): Define.
	* config/nds32/elf.h: New file.
	* config/nds32/linux.h: New file.
	* config/nds32/nds32-elf.opt: New file.
	* config/nds32/nds32-linux.opt: New file.
	* config/nds32/nds32-fp-as-gp.c
	(pass_nds32_fp_as_gp::gate): Consider TARGET_LINUX_ABI.
	* config/nds32/nds32.c (nds32_conditional_register_usage): Consider
	TARGET_LINUX_ABI.
	(nds32_asm_file_end): Ditto.
	(nds32_print_operand): Ditto.
	(nds32_insert_attributes): Ditto.
	(nds32_init_libfuncs): New function.
	(TARGET_HAVE_TLS): Define.
	(TARGET_INIT_LIBFUNCS): Define.
	* config/nds32/nds32.h (TARGET_DEFAULT_RELAX): Apply different relax
	spec content.
	(TARGET_ELF): Apply different mcmodel setting.
	(LINK_SPEC, LIB_SPEC, STARTFILE_SPEC, ENDFILE_SPEC): The content has
	been migrated into elf.h and linux.h files.
	* config/nds32/nds32.md (add_pc): Consider TARGET_LINUX_ABI.
	* config/nds32/nds32.opt (mvh): Consider TARGET_LINUX_ABI.
	(mcmodel): The content has been migrated into nds32-elf.opt and
	nds32-linux.opt files.
	* config/nds32/t-elf: New file.
	* config/nds32/t-linux: New file.

libgcc/
	* config.host (nds32*-linux*): New.
	* config/nds32/linux-atomic.c: New file.
	* config/nds32/linux-unwind.h: New file.

Co-Authored-By: Kito Cheng <kito.cheng@gmail.com>
Co-Authored-By: Monk Chiang <sh.chiang04@gmail.com>
From-SVN: r261116