include WORD_SIZE in tagfile content

this allows switching between 32 and 64 bit Julia without having to manually delete installed_vers

also use write instead of shelling out to echo, which is nonportable (it works on Windows only because we bundle busybox with the name echo.exe, ref https://github.com/timholy/HDF5.jl/commit/d531c088bd9dd8343069e4242f7a13569054feae - I plan on making sure this keeps working, but it relies on a GPL dependency and does require extra work on our side to make possible. Julia can't shell out to .bat files or cmd builtins due to limitations of libuv)