interpret format argument of QString::sprintf() as UTF-8

we expect our source code to be utf-8 throughout, so it doesn't make
sense to expect the specifier to be latin-1, as that limits the
effective charset to ascii.

Change-Id: I22335509ba6c5805d8b264cfd01d7f9a4cf7ef76
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/corelib/tools/qstring.cpp

@@ -5461,8 +5461,10 @@ QString &QString::vsprintf(const char* cformat, va_list ap)
     const char *c = cformat;
     for (;;) {
         // Copy non-escape chars to result
+        const char *cb = c;
         while (*c != '\0' && *c != '%')
-            result.append(QLatin1Char(*c++));
+            c++;
+        result.append(QString::fromUtf8(cb, (int)(c - cb)));
 
         if (*c == '\0')
             break;