atftp: build with gcc 5.2

atftp fails to build with gcc 5.2:

git/tftp_def.h:54:14: warning: inline function 'Strncpy' declared but never defined
git/argz.c:44:8: error: redefinition of 'argz_next'

GCC 5 defaults to -std=gnu11 instead of -std=gnu89. The semantics of
inline function changes. Pass '-std=gnu89' to gcc to compile atftp.

Ref:
https://gcc.gnu.org/gcc-5/porting_to.html

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>

meta-networking/recipes-daemons/atftp/atftp_git.bb

@@ -32,6 +32,8 @@ USERADD_PACKAGES = "${PN}d"
 USERADD_PARAM_${PN}d = "--system --no-create-home --shell /bin/false \
                         --user-group nobody"
 
+EXTRA_OEMAKE = "CFLAGS='${CFLAGS} -std=gnu89'"
+
 do_install_append() {
     install -d ${D}${sysconfdir}/init.d
     install -m 0755 ${WORKDIR}/atftpd.init ${D}${sysconfdir}/init.d/atftpd