[ARC] Update warning reporting.

MWDT compiler doesn't use eflags and makes use of 0x0c section. For
those, silence the gnu warning system.

bfd/
  Claudiu Zissulescu <claziss@synopsys.com>

        * elf32-arc.c (arc_elf_merge_private_bfd_data): Complain about
        efalgs only when in/out exists.
        (elf32_arc_section_from_shdr): Don't complain about 0x0c section
        type.  It is mwdt compiler specific.