[clang] [clang-repl] : Fix clang-repl crash with --cuda flag (PR #136404)

[Anutosh Bhat via cfe-commits]

================
@@ -760,8 +787,10 @@ std::unique_ptr<llvm::Module> Interpreter::GenModule() {
   return nullptr;
 }
 
-CodeGenerator *Interpreter::getCodeGen() const {
-  FrontendAction *WrappedAct = Act->getWrapped();
+CodeGenerator *Interpreter::getCodeGen(IncrementalAction *Action) const {
+  if (!Action)
+    Action = Act.get();
+  FrontendAction *WrappedAct = Action->getWrapped();
----------------
anutosh491 wrote:

Talking about changes with respect to codegen.

So errors like these 
```
./bin/clang-repl  --cuda
module flag identifiers must be unique (or of 'require' type)
!"wchar_size"
module flag identifiers must be unique (or of 'require' type)
!"nvvm-reflect-ftz"
module flag identifiers must be unique (or of 'require' type)
!"frame-pointer"
fatal error: error in backend: Broken module found, compilation aborted!
```
or even something like this 
```
error: Added modules have incompatible data layouts: e-p6:32:32-i64:64-i128:128-v16:16-v32:32-n16:32:64 (module) vs e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128 (jit)
```

Occur because we use the `Act` (the host IncrementalAction) to come up with the Module every time as of now.

But think about it when we are registering a PTU through registerPTU 

```
  if (!M)
    M = GenModule();
```
And we have this block. We shouldn't be generating the same Module for both the hostPTU (parsed through the incremental parser) and the devicePTU (parsed through the incrementalCudaParser) .

For the first case the Module should revolve around the triple `x86_64-unknown-linux-gnu` and for the device case the module should be framed around the target triple `nvptx64-nvidia-cuda`.

This is taken care of based on which `IncrementalAction` we use. We should use Act for hostPTU and DeviceACT for PTU. 

Hence the changes here (as one trickles into the other)
```
  CodeGenerator *getCodeGen(IncrementalAction *Action = nullptr) const;
  std::unique_ptr<llvm::Module> GenModule(IncrementalAction *Action = nullptr);
  PartialTranslationUnit &RegisterPTU(TranslationUnitDecl *TU,
                                      std::unique_ptr<llvm::Module> M = {},
                                      IncrementalAction *Action = nullptr);                                
```
So by default we use Act but we can take of it when required.

1) So while regiserting a devicePTU we use this https://github.com/llvm/llvm-project/pull/136404/files#diff-b8484f1fc5b057f146ed5d9b6e2cd47c3f6f5ae879c7a0eee44f0a272581a88cR580
2) While registering a hostptu we use this https://github.com/llvm/llvm-project/pull/136404/files#diff-b8484f1fc5b057f146ed5d9b6e2cd47c3f6f5ae879c7a0eee44f0a272581a88cR600





https://github.com/llvm/llvm-project/pull/136404