Add additional testing for 32bit variant of cygwin.

Add new script and config, `cygwin32`, to test 32bit variant of cygwin. Update existing
cygwin script and config to be `cygwin64`.

### TODO
* [x] Rename existing cygwin log files to cygwin64 to preserve history.
* [x] Verify that cygwin32 bat script works. (Confirmed by running with `CHPL_NIGHTLY_TEST_DIRS=release/examples/hello*.chpl`)
* [x] Add support for `cygwin32` and `cygwin64` platform values (see #955).