C++: Fix variable template parsing in expression

Fix parser to not fail on TemplateId without parentheses, for example:
int i = foo<int> + foo<char>;

This fixes std::pair structure parsing in MSVC headers and find Usages
to work with pair->first and pair->second.

Change-Id: Ic300ea99d44a749705430d5eb47b2744715af995
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

tests/auto/cplusplus/ast/tst_ast.cpp

@@ -173,6 +173,7 @@ private slots:
     //! "template<class ...Args> class T : Args... {};"
     void cpp11_variadic_inheritance();
     void cpp11_attributes();
+    void variableTemplatesInExpression();
 
     // Q_PROPERTY
     void cpp_qproperty();
@@ -1354,6 +1355,19 @@ void tst_AST::cpp11_attributes()
     QVERIFY(attr != nullptr);
 }
 
+void tst_AST::variableTemplatesInExpression()
+{
+    QSharedPointer<TranslationUnit> unit(parseDeclaration("int i = t<int> + t<char>;",
+                                                         false, false, true));
+    AST *ast = unit->ast();
+    QVERIFY(ast != nullptr);
+
+    QCOMPARE(diag.errorCount, 0);
+
+    DeclarationAST *d = ast->asDeclaration();
+    QVERIFY(d != nullptr);
+}
+
 void tst_AST::if_constexpr()
 {
     QSharedPointer<TranslationUnit> unit(parseStatement("if constexpr (a) b;",true));