libdfp: Update version for 1.0.9 release.
libdfp: Add generic macros and functions

This patch adds a header with generic macros and functions to transform
the _Decimal type to and from integer types.
libdfp: New <math.h> macro named issignaling to check for a signaling NaN (sNaN).

It is based on draft TS 18661 and this patch adds implementation for
both software based and PowerPC hardware dfp.