[ARC] Clean up arc header file.

[ARC] Clean up arc header file.

gcc/
2017-02-27  Claudiu Zissulescu  <claziss@synopsys.com>

	* config.gcc (arc*-): Clean up, use arc/big.h, arc/elf.h, and
	arc/linux.h headers.
	* config/arc/arc.h (TARGET_OS_CPP_BUILTINS): Remove.
	(LINK_SPEC): Likewise.
	(ARC_TLS_EXTRA_START_SPEC): Likewise.
	(EXTRA_SPECS): Likewise.
	(STARTFILE_SPEC): Likewise.
	(ENDFILE_SPEC): Likewise.
	(LIB_SPEC): Likewise.
	(TARGET_SDATA_DEFAULT): Likewise.
	(TARGET_MMEDIUM_CALLS_DEFAULT): Likewise.
	(MULTILIB_DEFAULTS): Likewise.
	(DWARF2_UNWIND_INFO): Likewise.
	* config/arc/big.h: New file.
	* config/arc/elf.h: Likewise.
	* config/arc/linux.h: Likewise.
	* config/arc/t-uClibc: Remove.

From-SVN: r245759