Update GATHER instructions to support 2 read-write operands. Patch from myself and Manman Ren.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160110 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/X86RecognizableInstr.h b/utils/TableGen/X86RecognizableInstr.h
index 6c0a234..542e510 100644
--- a/utils/TableGen/X86RecognizableInstr.h
+++ b/utils/TableGen/X86RecognizableInstr.h
@@ -204,7 +204,7 @@
                      unsigned &operandIndex,
                      unsigned &physicalOperandIndex,
                      unsigned &numPhysicalOperands,
-                     unsigned *operandMapping,
+                     const unsigned *operandMapping,
                      OperandEncoding (*encodingFromString)
                        (const std::string&,
                         bool hasOpSizePrefix));