package/feh: Fix build issue with some older cross-compilers
by adding -std=gnu99 to CFLAGS.
Fixes:
http://autobuild.buildroot.net/results/
392b58cca2671e206c85a530221ce7b2d42f31fb/
http://autobuild.buildroot.net/results/
94527fcd70fa85298c366537013c939534beead0/
http://autobuild.buildroot.net/results/
bf31199cdaa18971a9b599c26fbefac73b2d6f30/
http://autobuild.buildroot.net/results/
5b65c305b50664e02d5f8022278055c80739342d/
http://autobuild.buildroot.net/results/
ed3b9fb8d09cd677af4b8825566877c552926ae5/
Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>