sysusers: make sp_lstchg shadow field reproducible

If the environment variable SOURCE_DATE_EPOCH is set, use its value
instead of the current time.

src/basic/env-util.c

@@ -776,6 +776,18 @@ int getenv_bool_secure(const char *p) {
         return parse_boolean(e);
 }
 
+int getenv_uint64_secure(const char *p, uint64_t *ret) {
+        const char *e;
+
+        assert(p);
+
+        e = secure_getenv(p);
+        if (!e)
+                return -ENXIO;
+
+        return safe_atou64(e, ret);
+}
+
 int set_unset_env(const char *name, const char *value, bool overwrite) {
         assert(name);
 

src/basic/env-util.h

@@ -57,6 +57,8 @@ char *strv_env_pairs_get(char **l, const char *name) _pure_;
 int getenv_bool(const char *p);
 int getenv_bool_secure(const char *p);
 
+int getenv_uint64_secure(const char *p, uint64_t *ret);
+
 /* Like setenv, but calls unsetenv if value == NULL. */
 int set_unset_env(const char *name, const char *value, bool overwrite);