Tweaks to make sure it compiles on older raspian 8 (Jesse)

makefile

@@ -8,8 +8,7 @@ SRC=src
 # with debug:
 #CFLAGS:= $(CFLAGS) -O3 -Wall -g
 
-CFLAGS:= $(CFLAGS) -O3 -Wall
-
+CFLAGS:= $(CFLAGS) -std=c11 -O3 -Wall -D_POSIX_C_SOURCE
 all: objdir imgcomp
 
 objdir:

src/compare.c

@@ -10,6 +10,7 @@
 #include <stddef.h>
 #include <stdlib.h>
 #include <memory.h>
+#include <time.h>
 #include "imgcomp.h"
 #include "config.h"
 

src/compare_util.c

@@ -10,6 +10,7 @@
 #include <stddef.h>
 #include <stdlib.h>
 #include <memory.h>
+#include <time.h>
 #include "imgcomp.h"
 #include "config.h"
 

src/config.c

@@ -8,6 +8,7 @@
 #include <ctype.h>		// to declare isupper(), tolower() 
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include "imgcomp.h"
 #include "config.h"