Changes

Use the 64-bit version of the 64-bit compiler on Windows [ci skip].
Indeed, we used to use the 32-bit version in case we were running a
32-bit version of Windows, but by now everybody should be using a
64-bit version, so we may as well take advantage of the slightly more
efficient 64-bit version of the 64-bit compiler.
 (commit: 25e37e2)