[AD] sin, cos, sincos

["Vincent Penquerc'h" <Vincent.Penquerch@xxxxxxxxxx>]

Title: sin, cos, sincos

I've noticed, in math3d.c, that often sin and cos of a number are
used, so I've made a routine that gets both of them at a time, since
some CPUs have a faster way to get both at a time.
I've then noticed that rotate.c already was using it for DJGPP :)
Here's a patch that adds it.

I've moved the DJGPP call from rotate.c, but haven't tested it, since
I'm on Linux. The version for Linux GCC is commented out, since I
can't seem to be able to get the definition of either sincos or
__sincos (linux 2.2.10, glibc 2.1.1). Probably some define trickery
that needs to be added (I've tried USE_EXTERN_INLINES (IIRC)). It might
be different for other versions ?
There is a plain version for platforms that can't do it (eg it computes
both values separately).

The patch to imaths.h should be put in alinline.h, since I made
this on an already modified version of 3.9.39 (with my header splitting
thingie) and I didn't keep a copy of the original one :/

It's just something added at the end of the file though.

Cheers

--
Vincent Penquerc'h