code cleanup of named constants

zero, one, two, half are replaced by const literals
The policy was to use the f suffix for float consts (1.0f),
but don't use suffix for long double consts (these consts
can be exactly represented as double).

src/math/__tan.c

@@ -59,13 +59,9 @@ static const double T[] = {
              7.14072491382608190305e-05, /* 3F12B80F, 32F0A7E9 */
             -1.85586374855275456654e-05, /* BEF375CB, DB605373 */
              2.59073051863633712884e-05, /* 3EFB2A70, 74BF7AD4 */
-/* one */    1.00000000000000000000e+00, /* 3FF00000, 00000000 */
-/* pio4 */   7.85398163397448278999e-01, /* 3FE921FB, 54442D18 */
-/* pio4lo */ 3.06161699786838301793e-17  /* 3C81A626, 33145C07 */
-};
-#define one     T[13]
-#define pio4    T[14]
-#define pio4lo  T[15]
+},
+pio4 =       7.85398163397448278999e-01, /* 3FE921FB, 54442D18 */
+pio4lo =     3.06161699786838301793e-17; /* 3C81A626, 33145C07 */
 
 double __tan(double x, double y, int iy)
 {