Remove fpu_cordit2() and atanh_table[] completely.
Since cordit1 (for trigonometric functions) and cordit2 (for
hyperbolic functions) are very similar, so I implemented both
at first, but I didn't use cordit2 after all :(

Move fpu_cordit2() to #ifdef CORDIC_BOOTSTRAP section.
This reduces ~2KB text segment.
Reported by Krister Walfridsson on tech-kern two months ago.

branches: 1.2.4; 1.2.12; 1.2.16; 1.2.20;
s/tayler/taylor/. pointed out by christos@

Introduce the CORDIC algorithm.
o sine and cosine (e.g., FSIN, FCOS and FSINCOS instructions) is now
calculated in the CORDIC instead of Taylor expansion.
o tangent (FTAN) is not touched from a viewpoint of the code size.
o The CORDIC is applicable for hyperbolic functions (e.g., FSINH,
FCOSH, FTANH instructions), but I didn't use it because its working
range is poor.
o The CORDIC is also usable for inverse trigonometric functions,
I will commit it at next phase.
o The code size becomes a bit big. I cannot evaluate speed on m68k
for some reasons, but in test on i386 the CORDIC is approximately
100 times faster in sin/cos.