[openmp] Unconditionally set march commandline argument

[JonChesterfield]

Summary

Extracted from D117246. This reflects the march value used by the
compile back into the toolchain arguments, letting downstream processes
such as LTO rely on it being present. Subsequent patches should also be able
to remove the two other calls to checkSystemForAMDGPU.

[jhuber6]

LGTM, with this you should be able to replace calls for the AMDGPU arch with querying the ToolChain args, e.g. TCArgs.getLastArgValue(options::OPT_march_EQ)

[JonChesterfield]

Landed with you as author and me as reviewer as that seems a more accurate statement than the default. Thanks!

clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp

llvm::opt::DerivedArgList *AMDGPUOpenMPToolChain::TranslateArgs(
     Action::OffloadKind DeviceOffloadKind) const {
   DerivedArgList *DAL =
       HostTC.TranslateArgs(Args, BoundArch, DeviceOffloadKind);
   if (!DAL)
     DAL = new DerivedArgList(Args.getBaseArgs());
 
   const OptTable &Opts = getDriver().getOpts();
 
-  if (DeviceOffloadKind != Action::OFK_OpenMP) {
-    for (Arg *A : Args) {
+  if (DeviceOffloadKind == Action::OFK_OpenMP) {
+    for (Arg *A : Args)
+      if (!llvm::is_contained(*DAL, A))
         DAL->append(A);
-    }
+
+    std::string Arch = DAL->getLastArgValue(options::OPT_march_EQ).str();
+    if (Arch.empty()) {
+      checkSystemForAMDGPU(Args, *this, Arch);
+      DAL->AddJoinedArg(nullptr, Opts.getOption(options::OPT_march_EQ), Arch);
+    }
+
+    return DAL;
+
+  for (Arg *A : Args) {
+    DAL->append(A);
   }
 
   if (!BoundArch.empty()) {
     DAL->eraseArg(options::OPT_march_EQ);
     DAL->AddJoinedArg(nullptr, Opts.getOption(options::OPT_march_EQ),
                       BoundArch);
   }