Clarify usage of overloaded C++ function in MSVC++, which complains about its ambiguity.

Cython/Utility/Complex.c

@@ -279,7 +279,8 @@ static {{type}} __Pyx_PyComplex_As_{{type_name}}(PyObject* o) {
                 }
             } else {
                 r = __Pyx_c_abs{{func_suffix}}(a);
-                theta = atan2{{m}}(a.imag, a.real);
+                // MSVC++ seems to require the input casts.
+                theta = atan2{{m}}(({{real_type}})a.imag, ({{real_type}})a.real);
             }
             lnr = log{{m}}(r);
             z_r = exp{{m}}(lnr * b.real - theta * b.imag);

tests/run/complex_int_T446.pyx

@@ -2,8 +2,13 @@
 
 import cython
 
-cdef extern from "complex_int_T446_fix.h":
-    pass
+cdef extern from *:
+    """
+    #if defined _MSC_VER && defined __cplusplus
+    #define CYTHON_CCOMPLEX 0
+    #endif
+    """
+
 
 def test_arith(int complex a, int complex b):
     """

tests/run/complex_int_T446_fix.h

-#if defined _MSC_VER && defined __cplusplus
-#define CYTHON_CCOMPLEX 0
-#endif