C++: Support noexcept operator

The code model failed to parse the noexcept operator which is often
used in noexcept specifiers, e.g.: "void f() noexcept(noexcept(g()));"
Consequently some c++11 headers such as unordered_map, array
and unordered_set could not be parsed and no code completition was
available. I have created the NoExceptOperatorExpressionAST class
which is created whenever a noexcept token is found in an
expression with operator precedence. The noExcept test case
in the cplusplus/cxx11 test now contains a function that
uses the noexcept operator.

Fixed noexcept operator parsing

Added the test requested by Sergey Shambir, which then revealed that
i had not implemeneted the noexpect operator parsing according to the
c++ specification.
As stated here http://cpp0x.centaur.ath.cx/expr.unary.noexcept.html
the noexcept operator is a unary-expression that contains an
expression (and not a constant-expression). This should now be fixed.

Change-Id: Id4a99a43b660bd83e7680274491d99a698b57094
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/libs/cplusplus/FindUsages.cpp

@@ -1381,6 +1381,12 @@ bool FindUsages::visit(ThrowExpressionAST *ast)
     return false;
 }
 
+bool FindUsages::visit(NoExceptOperatorExpressionAST* ast)
+{
+    this->expression(ast->expression);
+    return false;
+}
+
 bool FindUsages::visit(TypeIdAST *ast)
 {
     for (SpecifierListAST *it = ast->type_specifier_list; it; it = it->next) {