[PATCH][AsmParser][MC] Allow asm parser to emit elf header flags

[Rafael Espíndola]

I spent some time reading the code that is already on trunk. It is a
pretty bad violation of the MC design, which is in part why this patch
looks odd.

What needs to happen is


+  MipsMCAsmFlags Flags;

This should be added to the streamer, not the parser. The parser a
really simple layer that driver the streamer. With that, then

  if (IDVal == ".abicalls") {
+    Flags.setRelocationModel(MipsMCAsmFlags::MAF_RM_CPIC);
+    if (Parser.getTok().isNot(AsmToken::EndOfStatement))
+      return Error(Parser.getTok().getLoc(), "unexpected token in directive");
+    return false;
+  }

Should call a emitAbitCalls method on the streamer.

And codegen should not have a   MipsELFStreamer::emitELFHeaderFlagsCG
and a MipsELFStreamer::emitELFHeaderFlagsAsm. That is the entire point
of having MC!

For this patch, at the very minimum you should transform

    EFlags |= ELF::EF_MIPS_CPIC;

to a call to  emitAbitCalls before   if (hasRawTextSupport()) in
emitELFHeaderFlagsCG.

I am sorry I missed emitELFHeaderFlagsCG when it went in. It should
never have happened.

Cheers,
Rafael