Align better with upstreamed fixes for clar (#776)

When upstreaming this patch to clar, the missing `localtime_r` symbol
was addressed in a different way. For details, see
clar-test/clar@ca0b519a. Let's use
that version instead.

Author: dscho

t/unit-tests/clar/clar.c

@@ -79,6 +79,8 @@
 #	else
 #		define p_snprintf snprintf
 #	endif
+
+#	define localtime_r(timer, buf) (localtime_s(buf, timer) == 0 ? buf : NULL)
 #else
 #	include <sys/wait.h> /* waitpid(2) */
 #	include <unistd.h>

t/unit-tests/clar/clar/summary.h

@@ -19,15 +19,6 @@ static int clar_summary_testsuites(struct clar_summary *summary)
 	return fprintf(summary->fp, "<testsuites>\n");
 }
 
-#ifdef _WIN32
-static struct tm *localtime_r(const time_t *timep, struct tm *result)
-{
-	if (localtime_s(result, timep) == 0)
-		return result;
-	return NULL;
-}
-#endif
-
 static int clar_summary_testsuite(struct clar_summary *summary,
     int idn, const char *name, time_t timestamp,
     int test_count, int fail_count, int error_count)