Add a test for range reduction of trigonometric functions on non-x86.
Trigonometric functions of large float arguments yield differing results
depending on how range reduction is done. There is already a test for
the results expected on x86, float.pure.lisp/(:range-reduction :x87).
Add a test for the results expected from GNU libm and enable it for
all platforms except x86. The new test is impure and therefore added
to "float.impure.lisp". Move the x86 test there, too, to reduce the
potential for future confusion.