Add support for the mips 'x' inline asm modifier.

Patch by Jack Carter.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157057 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/Mips/MipsAsmPrinter.cpp b/lib/Target/Mips/MipsAsmPrinter.cpp
index e62da35..3fa773b 100644
--- a/lib/Target/Mips/MipsAsmPrinter.cpp
+++ b/lib/Target/Mips/MipsAsmPrinter.cpp
@@ -383,6 +383,11 @@
           return true;
         O << "0x" << StringRef(utohexstr(MO.getImm())).lower();
         return false;
+      case 'x': // hex const int (low 16 bits)
+        if ((MO.getType()) != MachineOperand::MO_Immediate)
+          return true;
+        O << "0x" << StringRef(utohexstr(MO.getImm() & 0xffff)).lower();
+        return false;
     }
   }