[SYCL] Fix some uninitialized pointer usage in Driver (#1683)

Signed-off-by: gejin <[email protected]>

Author: jinge90

clang/lib/Driver/Driver.cpp

@@ -4741,7 +4741,7 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
       }
       UnbundlerInputs.push_back(LI);
     }
-    const Arg *LastArg;
+    const Arg *LastArg = nullptr;
     auto addUnbundlerInput = [&](types::ID T, const StringRef &A) {
       const llvm::opt::OptTable &Opts = getOpts();
       Arg *InputArg = MakeInputArg(Args, Opts, C.getArgs().MakeArgString(A));

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7726,7 +7726,8 @@ void SYCLPostLink::ConstructJob(Compilation &C, const JobAction &JA,
     addArgs(CmdArgs, TCArgs, {"-symbols"});
   }
   // specialization constants processing is mandatory
-  if (llvm::dyn_cast<SYCLPostLinkJobAction>(&JA)->getRTSetsSpecConstants())
+  auto *SYCLPostLink = llvm::dyn_cast<SYCLPostLinkJobAction>(&JA);
+  if (SYCLPostLink && SYCLPostLink->getRTSetsSpecConstants())
     addArgs(CmdArgs, TCArgs, {"-spec-const=rt"});
   else
     addArgs(CmdArgs, TCArgs, {"-spec-const=default"});