Since commit 70c2dc8a (Make compiler id detection more robust,
2008-03-10) we store compiler identification strings in test binaries
using the form

  char* info = "info";

Use the const-correct

  char const* info = "info";

form instead.  This allows the C++ compiler identification to work with
"-Werror -Wall" or equivalent flags if the compiler would warn about
const-to-non-const conversion.