Merge pull request #2373 from dscho/fix-t5516-flakiness

Fix t5516 flakiness in MSVC builds

Author: dscho

usage.c

@@ -9,10 +9,15 @@
 void vreportf(const char *prefix, const char *err, va_list params)
 {
 	char msg[4096];
-	size_t off = strlcpy(msg, prefix, sizeof(msg));
 	char *p, *pend = msg + sizeof(msg);
+	size_t prefix_len = strlen(prefix);
 
-	p = off < pend - msg ? msg + off : pend - 1;
+	if (sizeof(msg) <= prefix_len) {
+		fprintf(stderr, "BUG!!! too long a prefix '%s'\n", prefix);
+		abort();
+	}
+	memcpy(msg, prefix, prefix_len);
+	p = msg + prefix_len;
 	if (vsnprintf(p, pend - p, err, params) < 0)
 		*p = '\0'; /* vsnprintf() failed, clip at prefix */