Rename Start Menu folder for 32-bit installs on WoW64

Rename Start Menu folder for 32-bit installs on WoW64

This is not totally straightforward: Since setup can install Cygwin with
either bitness (using the '--arch 32|64' option), we must do the right
thing if this is a 64-bit installer being used to install 32-bit Cygwin,
which will run under WoW, even if the installer isn't...

(Naming things like this makes things consistent with Cygwin-X, which
already names it's Start Menu folder 'Cygwin-X (32-bit)' on WoW64. It
also ensures that there aren't collisions between any setup created
shortcuts for 32-bit and 64-bits.)

The desktop icon is already named 'Cygwin Terminal' or 'Cygwin64
Terminal' so doesn't need attention.

Start menu links made in the 'Cygwin' folder by cygwin-doc, and possibly
other packages will also need adjusting.