[Rd] Can R for Windows be built outside of the top-level source directory?

[Josh O'Brien]

The "R-admin" manual describes how to build R from outside of the
top-level source directory on a *NIX machine
(http://cran.r-project.org/doc/manuals/r-release/R-admin.html#Simple-compilation),
but it makes no analagous mention of a way to do so under Windows.
Since the build process in Windows is so different (not using
configure, for instance, and typically being performed from within
$R_SOURCES/src/gnuwin32/), *and* since the "R-admin" guide makes no
mention of it, my guess is that it's not easily possible. But I'd love
to learn otherwise, or even just get a definitive "no".

Thanks,

Josh