Desired Behavior

The variables accessible as part of the enabled_if field of the library stanza (and probably others like executable) only support a limited range of variables that does not include word_size. I think it would make sense to include it so that one can restrict the compilation of a library to 64-bit architectures, which makes sense if you rely, e.g., on an int counters not overflowing, but you do not want to pay the extra cost of using an Int64.t.