[SYCL] Fix double definition of default values for template parameters.

Added SuppressDefaultTemplateArguments flag for PrintingPolicy
class and use it at generation of the intergation header.

Example:
  ///  template<typename T = void>
  ///  class A {...};
  ///  /*Forward declaration*/
  ///  template<typename T> class kernel;
  ///  ...
  ///  cgh.parallel_for<class kernel<A>>>(
  ///      range<1>(1), [=](id<1> i){ /*do something*/ });

At the moment the forward declaration of class A will be generated as
  ///   template<typename T = void> class A
after this patch will be written as
  ///   template<typename T> class A

Signed-off-by: Vladimir Lazarev <vladimir.lazarev@intel.com>

clang/include/clang/AST/PrettyPrinter.h

@@ -52,7 +52,7 @@ struct PrintingPolicy {
         MSVCFormatting(false), ConstantsAsWritten(false),
         SuppressImplicitBase(false), FullyQualifiedName(false),
         RemapFilePaths(false), PrintCanonicalTypes(false),
-        SuppressDefinition(false) {}
+        SuppressDefinition(false), SuppressDefaultTemplateArguments (false) {}
 
   /// Adjust this printing policy for cases where it's known that we're
   /// printing C++ code (for instance, if AST dumping reaches a C++-only
@@ -69,6 +69,7 @@ struct PrintingPolicy {
   void adjustForCPlusPlusFwdDecl() {
     PolishForDeclaration = true;
     SuppressDefinition = true;
+    SuppressDefaultTemplateArguments = true;
   }
 
   /// The number of spaces to use to indent each line.
@@ -252,6 +253,15 @@ struct PrintingPolicy {
   ///   \endcode
   unsigned SuppressDefinition : 1;
 
+  /// When true, suppresses printing default template arguments of a type. E.g.
+  ///   \code
+  ///   template<typename T = void> class A
+  ///   \endcode
+  /// will be printed as
+  ///   \code
+  ///   template<typename T> class A
+  ///   \endcode
+  unsigned SuppressDefaultTemplateArguments : 1;
 };
 
 } // end namespace clang

clang/lib/AST/DeclPrinter.cpp

@@ -1014,7 +1014,8 @@ void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params) {
 
       Out << *TTP;
 
-      if (TTP->hasDefaultArgument()) {
+      if (TTP->hasDefaultArgument()
+          && !Policy.SuppressDefaultTemplateArguments ) {
         Out << " = ";
         Out << TTP->getDefaultArgument().getAsString(Policy);
       };
@@ -1024,7 +1025,8 @@ void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params) {
         Name = II->getName();
       printDeclType(NTTP->getType(), Name, NTTP->isParameterPack());
 
-      if (NTTP->hasDefaultArgument()) {
+      if (NTTP->hasDefaultArgument()
+          && !Policy.SuppressDefaultTemplateArguments ) {
         Out << " = ";
         NTTP->getDefaultArgument()->printPretty(Out, nullptr, Policy,
                                                 Indentation);

clang/test/CodeGenSYCL/integration_header.cpp

@@ -117,7 +117,7 @@ struct x {};
 template <typename T>
 struct point {};
 namespace second_namespace {
-template <typename T>
+template <typename T = int>
 class second_kernel;
 }