Revert "[SYCL] Support or diagnose use of namespace std types as kernel type names"

This reverts commit 46c54c6.

# Conflicts:
#	clang/test/CodeGenSYCL/stdtypes_kernel_type.cpp
#	clang/test/SemaSYCL/unnamed-kernel.cpp

Author: jtmott-intel

clang/lib/Sema/SemaSYCL.cpp

@@ -2727,27 +2727,30 @@ void SYCLIntegrationHeader::emitFwdDecl(raw_ostream &O, const Decl *D,
     auto *NS = dyn_cast_or_null<NamespaceDecl>(DC);
 
     if (!NS) {
-      const TagDecl *TD = isa<ClassTemplateDecl>(D)
-                              ? cast<ClassTemplateDecl>(D)->getTemplatedDecl()
-                              : dyn_cast<TagDecl>(D);
-      if (!TD)
-        break;
-
-      const bool KernelNameIsMissing = TD->getName().empty();
-      if (KernelNameIsMissing)
-        Diag.Report(KernelLocation, diag::err_sycl_kernel_incorrectly_named)
-            << /* kernel name is missing */ 0;
-      else if (!DC->isTranslationUnit()) {
-        // defined class constituting the kernel name is not globally
-        // accessible - contradicts the spec
-        if (!UnnamedLambdaSupport) {
-          if (TD->isCompleteDefinition())
+      if (!DC->isTranslationUnit()) {
+        const TagDecl *TD = isa<ClassTemplateDecl>(D)
+                                ? cast<ClassTemplateDecl>(D)->getTemplatedDecl()
+                                : dyn_cast<TagDecl>(D);
+
+        if (TD && !UnnamedLambdaSupport) {
+          // defined class constituting the kernel name is not globally
+          // accessible - contradicts the spec
+          const bool KernelNameIsMissing = TD->getName().empty();
+          if (KernelNameIsMissing) {
             Diag.Report(KernelLocation, diag::err_sycl_kernel_incorrectly_named)
-                << /* kernel name is not globally-visible */ 1;
-          else
-            Diag.Report(KernelLocation, diag::warn_sycl_implicit_decl);
-          Diag.Report(D->getSourceRange().getBegin(), diag::note_previous_decl)
-              << TD->getName();
+                << /* kernel name is missing */ 0;
+            // Don't emit note if kernel name was completely omitted
+          } else {
+            if (TD->isCompleteDefinition())
+              Diag.Report(KernelLocation,
+                          diag::err_sycl_kernel_incorrectly_named)
+                  << /* kernel name is not globally-visible */ 1;
+            else
+              Diag.Report(KernelLocation, diag::warn_sycl_implicit_decl);
+            Diag.Report(D->getSourceRange().getBegin(),
+                        diag::note_previous_decl)
+                << TD->getName();
+          }
         }
       }
       break;