Allow CONFIG_DEBUG_SYSLOG=y to be used

Instead of having to add the syslog define manually into CFLAGS,
CONFIG_DEBUG_SYSLOG=y can now be used in .config.

wpa_supplicant/Makefile

@@ -1089,6 +1089,10 @@ ifndef CONFIG_MAIN
 CONFIG_MAIN=main
 endif
 
+ifdef CONFIG_DEBUG_SYSLOG
+CFLAGS += -DCONFIG_DEBUG_SYSLOG
+endif
+
 ifdef CONFIG_DEBUG_FILE
 CFLAGS += -DCONFIG_DEBUG_FILE
 endif