[clang][driver] Fix null pointer dereference warning inside PrintActions1 (PR43462)

[RKSimon]

Summary

As detailed on PR43462, clang static analyzer is complaining about a null pointer dereference as we provide a 'host' toolchain fallback if the ToolChain pointer is null, but then use that pointer anyhow to report the triple.

Tests indicate the ToolChain pointer is always valid and the 'host' code path is redundant.

[ABataev]

LG

clang/lib/Driver/Driver.cpp

if (InputAction *IA = dyn_cast<InputAction>(A)) {
     os << "\"" << IA->getInputArg().getValue() << "\"";
   } else if (BindArchAction *BIA = dyn_cast<BindArchAction>(A)) {
     os << '"' << BIA->getArchName() << '"' << ", {"
        << PrintActions1(C, *BIA->input_begin(), Ids, SibIndent, SibKind) << "}";
   } else if (OffloadAction *OA = dyn_cast<OffloadAction>(A)) {
     bool IsFirst = true;
     OA->doOnEachDependence(
         [&](Action *A, const ToolChain *TC, const char *BoundArch) {
+          assert(TC && "Unknown host toolchain");
           // E.g. for two CUDA device dependences whose bound arch is sm_20 and
           // sm_35 this will generate:
           // "cuda-device" (nvptx64-nvidia-cuda:sm_20) {#ID}, "cuda-device"
           // (nvptx64-nvidia-cuda:sm_35) {#ID}
           if (!IsFirst)
             os << ", ";
           os << '"';
-          if (TC)
-            os << A->getOffloadingKindPrefix();
-          else
-            os << "host";
           os << " (";
           os << TC->getTriple().normalize();
-
           if (BoundArch)
             os << ":" << BoundArch;
           os << ")";
           os << '"';
           os << " {" << PrintActions1(C, A, Ids, SibIndent, SibKind) << "}";
           IsFirst = false;
           SibKind = OtherSibAction;
         });