[mips] Fix an initialization issue with MipsABIInfo in MipsTargetELFStreamer

[sdardis]

Summary

DebugInfoDWARFTests is the only user so far which initializes the
MCObjectStreamer without initializing the ASMParser. The MIPS backend
relies on the ASMParser to initialize the MipsABIInfo object and to
update the target streamer with it. This should turn the mips buildbots
green.

[sdardis]

I've tested this on a mips board, it can also be tested locally by modifying DWARFDebugInfoTest.cpp:getHostTripleForAddrSize to use "mipsel-unknown-linux-gnu" instead of LLVM_HOST_TRIPLE.

[sdardis]

Ping.

[sdardis]

Ping.

[atanasyan]

LGTM

llvm/trunk/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp

 //===-- MipsTargetStreamer.cpp - Mips Target Streamer Methods -------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file provides Mips specific target streamer methods.
 //
 //===----------------------------------------------------------------------===//
 
+#include "MCTargetDesc/MipsABIInfo.h"
 #include "MipsTargetStreamer.h"
 #include "InstPrinter/MipsInstPrinter.h"
 #include "MipsELFStreamer.h"
 #include "MipsMCExpr.h"
 #include "MipsMCTargetDesc.h"
 #include "MipsTargetObjectFile.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCSectionELF.h"
MipsTargetELFStreamer::MipsTargetELFStreamer(MCStreamer &S,
   // b: There aren't any usage paths that initialize the ABI
   //    pointer until after we initialize either an assembler
   //    or the target machine.
   // We can fix this by making the target streamer construct
   // the ABI, but this is fraught with wide ranging dependency
   // issues as well.
   unsigned EFlags = MCA.getELFHeaderEFlags();
 
+  // FIXME: Fix a dependency issue by instantiating the ABI object to some
+  // default based off the triple. The triple doesn't describe the target
+  // fully, but any external user of the API that uses the MCTargetStreamer
+  // would otherwise crash on assertion failure.
+
+  ABI = MipsABIInfo(
+      STI.getTargetTriple().getArch() == Triple::ArchType::mipsel ||
+              STI.getTargetTriple().getArch() == Triple::ArchType::mips
+          ? MipsABIInfo::O32()
+          : MipsABIInfo::N64());
+
   // Architecture
   if (Features[Mips::FeatureMips64r6])
     EFlags |= ELF::EF_MIPS_ARCH_64R6;
   else if (Features[Mips::FeatureMips64r2] ||
            Features[Mips::FeatureMips64r3] ||
            Features[Mips::FeatureMips64r5])
     EFlags |= ELF::EF_MIPS_ARCH_64R2;
   else if (Features[Mips::FeatureMips64])