package/keepalived: fix build with gcc < 4.9

Disable track-process to avoid the following build failure with
gcc < 4.9 raised since bump to version 2.2.7 in commit
79f631000fe6846e72f44810452bb764c228ad44 as suggested by upstream in
https://github.com/acassen/keepalived/issues/2094:

In file included from ../../lib/rbtree.h:24:0,
                 from ../../lib/rbtree_ka.h:26,
                 from ../../lib/scheduler.h:40,
                 from ../../lib/notify.h:31,
                 from ../../keepalived/include/vrrp.h:41,
                 from ../../keepalived/include/track_process.h:31,
                 from track_process.c:50:
../../lib/rbtree_types.h:31:25: error: initializer element is not constant
 #define RB_ROOT (struct rb_root) { NULL, }
                         ^

Fixes:
 - http://autobuild.buildroot.org/results/2132570fb0407abc0e70146d771471e13ef10237

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/keepalived/keepalived.mk

@@ -56,4 +56,8 @@ else
 KEEPALIVED_CONF_OPTS += --disable-nftables
 endif
 
+ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_4_9),)
+KEEPALIVED_CONF_OPTS += --disable-track-process
+endif
+
 $(eval $(autotools-package))