inline constant into its single use

Modules/_math.c

@@ -22,7 +22,6 @@
 static const double ln2 = 6.93147180559945286227E-01;
 static const double two_pow_m28 = 3.7252902984619141E-09; /* 2**-28 */
 static const double two_pow_p28 = 268435456.0; /* 2**28 */
-static const double zero = 0.0;
 
 /* acosh(x)
  * Method :
@@ -143,7 +142,7 @@ _Py_atanh(double x)
 #ifdef Py_NAN
         return Py_NAN;
 #else
-        return x/zero;
+        return x/0.0;
 #endif
     }
     if (absx < two_pow_m28) {           /* |x| < 2**-28 */