restore PromoteKernelArg pass (llvm#1908)

Author: ronlieb

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -892,6 +892,13 @@ void AMDGPUTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB) {
 
   PB.registerFullLinkTimeOptimizationLastEPCallback(
       [this](ModulePassManager &PM, OptimizationLevel Level) {
+
+        // Promote kernel arguments to global address space for LLVM IR
+        // generated by flang compiler
+        FunctionPassManager FPM;
+        FPM.addPass(AMDGPUPromoteKernelArgumentsPass());
+        PM.addPass(createModuleToFunctionPassAdaptor(std::move(FPM)));
+
         // When we are using -fgpu-rdc, we can only run accelerator code
         // selection after linking to prevent, otherwise we end up removing
         // potentially reachable symbols that were exported as external in other