[clang] [Clang][OpenCL][AMDGPU] Allow a kernel to call another kernel (PR #115821)

[Shilei Tian via cfe-commits]

================
@@ -196,13 +203,21 @@ class GlobalDecl {
   }
 
   GlobalDecl getWithKernelReferenceKind(KernelReferenceKind Kind) {
-    assert(isa<FunctionDecl>(getDecl()) &&
-           cast<FunctionDecl>(getDecl())->hasAttr<CUDAGlobalAttr>() &&
-           "Decl is not a GPU kernel!");
+    assert((isa<FunctionDecl>(getDecl()) &&
+            cast<FunctionDecl>(getDecl())->hasAttr<CUDAGlobalAttr>() &&
+            "Decl is not a GPU kernel!") ||
+           (isDeclOpenCLKernel() && "Decl is not a OpenCL kernel!"));
     GlobalDecl Result(*this);
     Result.Value.setInt(unsigned(Kind));
     return Result;
   }
+
+  bool isDeclOpenCLKernel() const {
+    auto FD = dyn_cast<FunctionDecl>(getDecl());
+    if (FD)
+      return FD->hasAttr<OpenCLKernelAttr>();
+    return FD;
+  }
----------------
shiltian wrote:

```suggestion
  bool isDeclOpenCLKernel() const {
    if (auto FD = dyn_cast<FunctionDecl>(getDecl()))
      return FD->hasAttr<OpenCLKernelAttr>();
    return false;
  }
```

https://github.com/llvm/llvm-project/pull/115821