[llc] Initialize TargetLoweringObjectFile for MIR input

MIRParser uses MC and transitively calls MCObjectFileInfo::getObjectFileType().
TargetLoweringObjectFile::Initialize should be called beforehand to
initialize MCObjectFileInfo::Env.

This manifested as a -fsanitize=undefined
test/CodeGen/MIR/X86/instr-symbols-and-mcsymbol-operands.mir failure
when D71360/aa5ee8f244441a8ea103a7e0ed8b6f3e74454516 was committed.

Author: MaskRay

llvm/tools/llc/llc.cpp

@@ -50,6 +50,7 @@
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Support/WithColor.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include <memory>
@@ -598,6 +599,8 @@ static int compileModule(char **argv, LLVMContext &Context) {
 
     if (MIR) {
       assert(MMIWP && "Forgot to create MMIWP?");
+      const_cast<TargetLoweringObjectFile *>(LLVMTM.getObjFileLowering())
+          ->Initialize(MMIWP->getMMI().getContext(), *Target);
       if (MIR->parseMachineFunctions(*M, MMIWP->getMMI()))
         return 1;
     }