lib: add mktime64() for linux compatibility

This function will be used  in lib/crypto/x509_cert_parser.c, which
will also be imported from linux code in a later commit.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
diff --git a/include/linux/time.h b/include/linux/time.h
index b8d298e..dc9344a 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -1,6 +1,7 @@
 #ifndef _LINUX_TIME_H
 #define _LINUX_TIME_H
 
+#include <rtc.h>
 #include <linux/types.h>
 
 #define _DEFUN(a,b,c) a(c)
@@ -150,4 +151,13 @@
     return asctime_r (localtime_r (tim_p, &tm), result);
 }
 
+/* for compatibility with linux code */
+typedef __s64 time64_t;
+
+#ifdef CONFIG_LIB_DATE
+time64_t mktime64(const unsigned int year, const unsigned int mon,
+		  const unsigned int day, const unsigned int hour,
+		  const unsigned int min, const unsigned int sec);
+#endif
+
 #endif