Commit 65abaab547 tried to prevent the scaling constants used in
the degree-based trig functions from being precomputed at compile time,
because some compilers do that with functions that don't yield results
identical-to-the-last-bit to what you get at runtime. A report from
Peter Eisentraut suggests that some recent compilers are smart enough
to see through that trick, though. Instead, let's put the inputs to
these calculations into non-const global variables, which should be a
more reliable way of convincing the compiler that it can't assume that
they are compile-time constants. (If we really get desperate, we could
mark these variables "volatile", but I do not believe we should have to.)
6b1a213bbd