[Instrumentation] Fix a warning

This patch fixes:

  llvm/lib/Transforms/Instrumentation/NumericalStabilitySanitizer.cpp:1528:38:
  error: unused variable 'TableRef' [-Werror,-Wunused-variable]

Author: kazutakahirata

llvm/lib/Transforms/Instrumentation/NumericalStabilitySanitizer.cpp

@@ -1529,6 +1529,7 @@ Value *NumericalStabilitySanitizer::maybeHandleKnownCallBase(
   assert(Intrinsic::matchIntrinsicSignature(WidenedFnTy, TableRef, ArgTys) ==
              Intrinsic::MatchIntrinsicTypes_Match &&
          "invalid widened intrinsic");
+  (void)TableRef;
   // For known intrinsic functions, we create a second call to the same
   // intrinsic with a different type.
   SmallVector<Value *, 4> Args;