ext: Update fputils to rev 13589cd

This patch updates fputils to the latest revision (13589cd) from the
upstream repository (github.com/andysan/fputils).

ext: Update fputils to rev 6a47fd8358

This patch updates fputils to the latest revision (6a47fd8358) from
the upstream repository (github.com/andysan/fputils). Most notably,
this includes changes that export a limited set of 64-bit float
manipulation and avoids a warning about unused 64-bit floats in clang.

ext: Update fputils to rev 52b6190b4e

This changeset updates the external library to git revision
52b6190b4e. This update includes changes that fix compilation errors
on old gcc versions and fixes to test a case that affect ICC.

ext: Include libfputils

This changeset includes libfputils from revision bbf0d61d75. This
library can be used to convert to and from 80-bit floats and query the
type of an 80-bit float, which is needed to support the x87 FPU.