[Clang] Fix warning on unused varaible

Summary:
Don't check the flag this way, it leads to unused variables. Fix.

Author: jhuber6

clang/lib/Driver/ToolChains/Clang.cpp

@@ -8429,7 +8429,8 @@ void LinkerWrapper::ConstructJob(Compilation &C, const JobAction &JA,
   Args.ClaimAllArgs(options::OPT_Xoffload_linker);
 
   // Embed bitcode instead of an object in JIT mode.
-  if (const Arg *A = Args.getLastArg(options::OPT_fopenmp_target_jit))
+  if (Args.hasFlag(options::OPT_fopenmp_target_jit,
+                   options::OPT_fno_openmp_target_jit, false))
     CmdArgs.push_back("--embed-bitcode");
 
   // Forward `-mllvm` arguments to the LLVM invocations if present.