Fix float support on vxWorks.

Thanks to Dustin Spicuzza. Fixes #2957

Merged revisions 52481 via svnmerge from 
https://svn.boost.org/svn/boost/trunk


[SVN r52517]

libs/functional

@@ -1 +1 @@
-Subproject commit 8a4506cca3741a56abf17921888f776897c78d23
+Subproject commit c09efebd3205bfbf2917a6c678fdc4193a6bf550