mtd-utils/mkfs.jffs2: honor env SOURCE_DATE_EPOCH

Use the timestamp from the enviroment SOURCE_DATE_EPOCH
if set instead of the build time.

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>

tools/mtd-utils/patches/320-mkfs.jffs2-SOURCE_DATE_EPOCH.patch

+Index: mtd-utils-1.5.2/mkfs.jffs2.c
+===================================================================
+--- mtd-utils-1.5.2.orig/mkfs.jffs2.c
++++ mtd-utils-1.5.2/mkfs.jffs2.c
+@@ -108,7 +108,7 @@ static char *rootdir = default_rootdir;
+ static int verbose = 0;
+ static int squash_uids = 0;
+ static int squash_perms = 0;
+-static int fake_times = 0;
++static time_t fixed_timestamp = -1;
+ int target_endian = __BYTE_ORDER;
+ 
+ uint32_t find_hardlink(struct filesystem_entry *e)
+@@ -249,8 +249,8 @@ static struct filesystem_entry *add_host
+ 			mode &= ~(S_ISUID | S_ISGID);
+ 		}
+ 	}
+-	if (fake_times) {
+-		timestamp = 0;
++	if (fixed_timestamp != -1) {
++		timestamp = fixed_timestamp;
+ 	}
+ 
+ 	entry = xcalloc(1, sizeof(struct filesystem_entry));
+@@ -1554,6 +1554,20 @@ void parse_image(){
+ 	close(in_fd);
+ }
+ 
++static void set_source_date_epoch() {
++	char *env = getenv("SOURCE_DATE_EPOCH");
++	char *endptr = env;
++	errno = 0;
++	if (env && *env) {
++		fixed_timestamp = strtoull(env, &endptr, 10);
++		if (errno || (endptr && *endptr != '\0')) {
++			fprintf(stderr, "Invalid SOURCE_DATE_EPOCH");
++			exit(1);
++		}
++	}
++}
++
++
+ int main(int argc, char **argv)
+ {
+ 	int c, opt;
+@@ -1572,6 +1586,7 @@ int main(int argc, char **argv)
+ 		warn_page_size = 1; /* warn user if page size not 4096 */
+ 
+ 	jffs2_compressors_init();
++	set_source_date_epoch();
+ 
+ 	while ((opt = getopt_long(argc, argv,
+ 					"D:d:r:s:o:qUPfh?vVe:lbp::nc:m:x:X:Lty:i:", long_options, &c)) >= 0)
+@@ -1622,7 +1637,7 @@ int main(int argc, char **argv)
+ 				break;
+ 
+ 			case 'f':
+-				fake_times = 1;
++				fixed_timestamp = 0;
+ 				break;
+ 
+ 			case 'h':