Related with bug 86829, but for hyperbolic trigonometric functions.
This patch adds substitution rules to both sinh(tanh(x)) -> x / sqrt(1
- x*x) and cosh(tanh(x)) -> 1 / sqrt(1 - x*x). Notice that the both
formulas has division by 0, but it causes no harm because 1/(+0) ->
+infinity, thus the math is still safe.

Changelog:
2018-08-07  Giuliano Belinassi <giuliano.belinassi@usp.br>

    * match.pd: add simplification rules to sinh(atanh(x)) and cosh(atanh(x)).

All tests added by this patch runs without errors in trunk, however,
there are tests unrelated with this patch that fails in my x86_64
Ubuntu 18.04.