[SYCL] Implement no-decomposition for kernel types that don't need it.

clang/include/clang/Basic/Attr.td

@@ -1198,6 +1198,14 @@ def SYCLIntelBufferLocation : InheritableAttr {
   let Documentation = [Undocumented];
 }
 
+def SYCLRequiresDecomposition : InheritableAttr {
+  // No spellings, as this is for internal use.
+  let Spellings = [];
+  let Subjects = SubjectList<[Named]>;
+  let LangOpts = [SYCLIsDevice, SYCLIsHost];
+  let Documentation = [Undocumented];
+}
+
 def SYCLIntelKernelArgsRestrict : InheritableAttr {
   let Spellings = [ CXX11<"intel", "kernel_args_restrict"> ];
   let Subjects = SubjectList<[Function], ErrorDiag>;