Add missing constructor to CPPLanguage.

CPPLanguage is missing a user defined constructor,
but in language.cc a const variable of this type is defined.

This is not valid c++. Since is non-POD as it has a base class and from the
standard:

From the standard:

[class] p4

A POD-struct is an aggregate class that has no non-static data members of type
non-POD-struct, non-POD-union (or array of such types) or reference, and has no
user-declared copy assignment operator and no user-declared destructor.

[dcl.init.aggr]

An aggregate is an array or a class (clause 9) with no user-declared
constructors (12.1), no private or protected non-static data members (clause
11), no base classes (clause 10), and no virtual functions (10.3).


For more information see.
http://clang.llvm.org/compatibility.html#default_init_const