pl/math: Fix fp exceptions in Neon sinhf and sinh

Both routines previously relied on the vector expm1(f) routine exposed
by the library, which depended on WANT_SIMD_EXCEPT for its fenv
behaviour, however both routines were expected to always trigger fp
exceptions correctly. To remedy this, both routines now use an inlined
helper for expm1 (reused from vector tanhf in the case of sinhf), and
special-case small input as well as large when WANT_SIMD_EXCEPT is
enabled.