Fix building tst_dialogs against libc++

Linking fails if re2 was built against libstdc++.

Change-Id: I69868ff284c8d23ccd7219f4da6ec750ff7674b9
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

config.tests/re2/re2.cpp

@@ -30,6 +30,7 @@
 
 int main(int, char **)
 {
-    RE2 re2("dummytest");
+    std::string s("dummytest");
+    RE2 re2(s);
     return 0;
 }