Updated gcc-4.9 packages has been released for Debian GNU/Linux 8 LTS

Package : gcc-4.9
Version : 4.9.2-10+deb8u2
Debian Bug : 727621

This update fixes libstdc++ std::future support on armel, which is
necessary to get firefox-esr and thunderbird updates built on that
architecture.

For Debian 8 "Jessie", this problem has been fixed in version
4.9.2-10+deb8u2.

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://wiki.debian.org/LTS

  GCC-4.9 Bugfix Update for Debian 8 LTS