next step on moving Windows build to external libs

git-svn-id: https://svn.r-project.org/R/trunk@67143 00db46b3-68df-0310-9c12-caf00c1e9a41
clean up

git-svn-id: https://svn.r-project.org/R/trunk@67144 00db46b3-68df-0310-9c12-caf00c1e9a41
tweak

git-svn-id: https://svn.r-project.org/R/trunk@67145 00db46b3-68df-0310-9c12-caf00c1e9a41