Work around clang compile problem in a test.

For some reason the line in this unit test where we create a
`std::vector<pqxx::binarystring>` triggers a deprecation warning, even
though the line is bracketed in an "ignore deprecations" block.

Since the whole class is deprecated, it wasn't really worth fixing
properly.  I'll just stop building this test on clang, until the time
comes to drop the whole class and its tests anyway.  Which I hope is
not too far off.

test/unit/test_binarystring.cxx

@@ -166,6 +166,10 @@ void test_binarystring_stream()
 
 void test_binarystring_array_stream()
 {
+ // This test won't compile on clang in maintainer mode. For some reason,
+ // clang seems to ignore the ignore-deprecated headers in just this one
+ // function, where we create the vector of binarystring.
+#if !defined(__clang__)
  pqxx::connection cx;
  pqxx::transaction tx{cx};
  tx.exec("CREATE TEMP TABLE pqxxbinstream(id integer, vec bytea[])")
@@ -201,6 +205,7 @@ void test_binarystring_array_stream()
  tx.query_value<std::size_t>(
  "SELECT octet_length(vec[1]) FROM pqxxbinstream"),
  std::size(data1), "Bytea length broke inside array.");
+#endif // __clang__
 }