[WebAssembly] Fix warnings

This patch fixes:

  llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp:126:26:
  error: lambda capture 'DAG' is not used
  [-Werror,-Wunused-lambda-capture]

  llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp:239:28:
  error: unused variable 'Info' [-Werror,-Wunused-variable]

Author: kazutakahirata

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

@@ -123,7 +123,7 @@ static SDValue getTagSymNode(int Tag, SelectionDAG *DAG) {
 static APInt encodeFunctionSignature(SelectionDAG *DAG, SDLoc &DL,
                                      SmallVector<MVT, 4> &Returns,
                                      SmallVector<MVT, 4> &Params) {
-  auto toWasmValType = [&DAG, &DL](MVT VT) {
+  auto toWasmValType = [&](MVT VT) {
     if (VT == MVT::i32) {
       return wasm::ValType::I32;
     }

llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp

@@ -239,6 +239,7 @@ void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
       const MCOperandInfo &Info = Operands[DescIndex];
       assert(Info.OperandType == WebAssembly::OPERAND_TYPEINDEX &&
              "unexpected CImmediate operand");
+      (void)Info;
       MCOp = lowerEncodedFunctionSignature(MO.getCImm()->getValue());
       break;
     }