libm: cherry-pick one patch from freebsd to fix logb() denormals issue

libm: cherry-pick one patch from freebsd to fix logb() denormals issue

from http://svnweb.freebsd.org/base?view=revision&revision=176101
"
Oops, fix the fix in rev.1.10.  logb() and logbf() were broken on
 denormals, and logb() remained broken after 1.10 because the fix for
 logbf() was incompletely translated.

Convert to __FBSDID().
"

Change-Id: I54f33648db7c421b06eee1ea8e63c57a179fae0d
Signed-off-by: Jack Ren <jack.ren@intel.com>
Signed-off-by: Jin Wei <wei.a.jin@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>