PR libstdc++/60936 fix length calculation

	PR libstdc++/60936
	* src/c++11/snprintf_lite.cc (__concat_size_t): Calculate length
	written to buffer, not length remaining in buffer.

From-SVN: r245505

libstdc++-v3/ChangeLog

+2017-02-16  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/60936
+	* src/c++11/snprintf_lite.cc (__concat_size_t): Calculate length
+	written to buffer, not length remaining in buffer.
+
 2017-02-15  Tim Shen  <timshen@google.com>
 
 	PR libstdc++/78723

libstdc++-v3/src/c++11/snprintf_lite.cc

@@ -81,7 +81,7 @@ namespace __gnu_cxx {
 	__val /= 10;
       }
     while (__val != 0);
-    size_t __len = __out - __cs;
+    size_t __len = __cs + __ilen - __out;
     if (__bufsize < __len)
       return -1;