[cxx-interop] Simplify name generation for template arguments of builtin types

We were searching for types in the Swift stdlib by name, just to get the names back from the types. Let's just return the type name without performing the search.

No user-facing change intended.

Author: egorzhdan

lib/ClangImporter/ClangClassTemplateNamePrinter.cpp

@@ -35,33 +35,19 @@ struct TemplateInstantiationNamePrinter
   }
 
   std::string VisitBuiltinType(const clang::BuiltinType *type) {
-    Type swiftType = nullptr;
     switch (type->getKind()) {
     case clang::BuiltinType::Void:
-      swiftType =
-          swiftCtx.getNamedSwiftType(swiftCtx.getStdlibModule(), "Void");
-      break;
+      return "Void";
+
 #define MAP_BUILTIN_TYPE(CLANG_BUILTIN_KIND, SWIFT_TYPE_NAME)                  \
-      case clang::BuiltinType::CLANG_BUILTIN_KIND:                             \
-        swiftType = swiftCtx.getNamedSwiftType(swiftCtx.getStdlibModule(),     \
-                                               #SWIFT_TYPE_NAME);              \
-        break;
-#define MAP_BUILTIN_CCHAR_TYPE(CLANG_BUILTIN_KIND, SWIFT_TYPE_NAME)            \
-      case clang::BuiltinType::CLANG_BUILTIN_KIND:                             \
-        swiftType = swiftCtx.getNamedSwiftType(swiftCtx.getStdlibModule(),     \
-                                               #SWIFT_TYPE_NAME);              \
-        break;
+    case clang::BuiltinType::CLANG_BUILTIN_KIND:                               \
+      return #SWIFT_TYPE_NAME;
 #include "swift/ClangImporter/BuiltinMappedTypes.def"
     default:
       break;
     }
 
-    if (swiftType) {
-      if (swiftType->is<NominalType>() || swiftType->isVoid()) {
-        return swiftType->getStringAsComponent();
-      }
-    }
-    return "_";
+    return VisitType(type);
   }
 
   std::string VisitTagType(const clang::TagType *type) {