'secure_getenv' api is not uniformly implemented across all C libraries
therefore its good to include missing.h so it can use the alternative
implementation where its not awvailable
Fixes
../git/src/login/pam_systemd.c:344:13: error: implicit declaration of function 'secure_getenv' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
v = secure_getenv(key);
Signed-off-by: Khem Raj <raj.khem@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
