[ARC] Add linker relaxation.

[ARC] Add linker relaxation.

Add linker relaxation. The first relaxation added is converting
GOTPC32 to PCREL relocations. This relaxation doesn't change the size of
the binary.

bfd/
xxxx-xx-xx  Claudiu Zissulescu  <claziss@synopsys.com>

	* elf32-arc.c (bfd_get_32_me): New function.
	(bfd_put_32_me): Likewise.
	(arc_elf_relax_section): Likewise.
	(bfd_elf32_bfd_relax_section): Define.

ld/testsuite/
xxxx-xx-xx  Claudiu Zissulescu  <claziss@synopsys.com>

	* ld-arc/relax-local-pic.d: New test.
	* ld-arc/relax-local-pic.s: New file.