Use pedantically correct definition of _POSIX_C_SOURCE (reported to upstream)
Index: utils/sundazel.c
--- utils/sundazel.c.orig
+++ utils/sundazel.c
@@ -95,7 +95,7 @@ char usage[] =
 "effective.\n";
 
 // To get the declaration of localtime_r() from time.h.
-#define _POSIX_C_SOURCE 1
+#define _POSIX_C_SOURCE 199506L
 
 #include <math.h>
 #include <time.h>