MFC r257770 r257818 r257823 r260066 r260067 r260089 r260145 r268587 r268588
    r268589 r268590 r268593 r268597 r269758 r270845 r270847 r270893 r270932
    r270947 r271147

Merge libm work by kargl, bde and das from the past few months.
Besides optimisations and small bug fixes this includes new implementations
for C99 functions expl, coshl, sinhl, tanhl, erfl and erfcl.

Approved by:	re (kib)