[patch] Add discriminator support to gas .loc directive

[Cary Coutant]

>>        * NEWS: Add item about discriminator support.
>>        * dwarf2dbg.h (struct dwarf2_line_info): Add discriminator field.
>>        * dwarf2dbg.c (current): Add discriminator field.
>>        (dwarf2_where): Copy discriminator value.
>>        (dwarf2_consume_line_info): Set discriminator to 0.
>>        (dwarf2_directive_loc): Process discriminator sub-op.
>>        (out_leb128): New function.
>>        (process_entries): Output DW_LNE_set_discriminator.
>>        * doc/as.texinfo: Add discriminator operand to .loc directive.
>>        * testsuite/gas/lns/lns-common-1.d: Add test for discriminator.
>>        * testsuite/gas/lns/lns-common-1.s: Likewise.
>
> Approved - please apply.

Thanks! Committed.

-cary