HAVE_UV_IMPORT and other config.h macros must not be set unconditionally
because no existing libuv release exposes uv_import() and/or uv_export()
yet. Windows builds not passing an explicit path to libuv to
win32utils/Configure are currently broken because of this, so comment
out the offending lines and describe when the aforementioned config.h
macros should be set.
(cherry picked from commit 57b430b8ca)
11f2f7bfbf