autobuild 1.1 now supports expanding $variables within a config file --
support that was explicitly added to address this very problem. So now the
windows platform in autobuild.xml uses $AUTOBUILD_ADDRSIZE,
$AUTOBUILD_WIN_VSPLATFORM and $AUTOBUILD_WIN_CMAKE_GEN, which should handle
most of the deltas between the windows platform and windows64.

This permits removing the windows64 platform definition from autobuild.xml.

The one remaining delta between the windows64 and windows platform definitions
was -DLL_64BIT_BUILD=TRUE. But we can handle that instead by checking
ADDRESS_SIZE. Change all existing references to WORD_SIZE to ADDRESS_SIZE
instead, and set ADDRESS_SIZE to $AUTOBUILD_ADDRSIZE. Change the one existing
LL_64BIT_BUILD reference to test (ADDRESS_SIZE EQUAL 64) instead.