Disable date object related system calls by default

Use DATE_SYS_CALLS=ON for make target to enable the
date related system calls. Also fix some minor issues.
Related issue: #923

JerryScript-DCO-1.0-Signed-off-by: László Langó llango.u-szeged@partner.samsung.com

jerry-libc/include/sys/time.h

@@ -31,6 +31,15 @@ struct timeval
   unsigned long tv_usec;  /**< microseconds */
 };
 
+/**
+ * Timezone structure
+ */
+struct timezone
+{
+  int tz_minuteswest;     /**< minutes west of Greenwich */
+  int tz_dsttime;         /**< type of DST correction */
+};
+
 int gettimeofday (void *tp, void *tzp);
 
 #ifdef __cplusplus