Clarify types in atan2() call for usage in MSVC++.

Cython/Utility/Complex.c

@@ -275,7 +275,7 @@ static {{type}} __Pyx_PyComplex_As_{{type_name}}(PyObject* o) {
                     theta = 0;
                 } else {
                     r = -a.real;
-                    theta = atan2{{m}}(0, -1);
+                    theta = atan2{{m}}(0.0, -1.0);
                 }
             } else {
                 r = __Pyx_c_abs{{func_suffix}}(a);