78.4.0esr-based build is busted on Linux

17:59.53
/var/tmp/build/firefox-9633b5c7e832/security/sandbox/linux/SandboxFilter.cpp:247:36:
error: use of undeclared identifier 'AT_EMPTY_PATH'
17:59.53     if (fd != AT_FDCWD && (flags & AT_EMPTY_PATH) != 0 &&
17:59.53                                    ^

Wheezy comes with glibc 2.13 but AT_EMPTY_PATH showed up in 2.14 first.