uclibc_git.bb: Enable backtrace and fenv

Upgrade to latest snapshot to bring in libubacktrace
and enable it since e-wm needs it. Also enable fenv
to compiler target gcc.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>