compiler/glsl: fix precision problem of tanh

compiler/glsl: fix precision problem of tanh

Clamp input scalar value to range [-10, +10] to avoid precision problems
when the absolute value of input is too large.

Fixes dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.* test
failures.

v2: added more explanation in the comment.
v3: fixed a typo in the comment.

Signed-off-by: Haixia Shi <hshi@chromium.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "13.0" <mesa-dev@lists.freedesktop.org>