databases/xapian-core10: Fix build with Clang 6
Too many errors to reasonably patch like
backends/flint/flint_database.cc:813:61: error: invalid suffix on literal; C++11 requires a space between literal and identifier [-Wreserved-user-defined-literal]
throw Xapian::InvalidArgumentError("Term too long (> "STRINGIZE(MAX_SAFE_TERM_LENGTH)"): " + tname);
^