Revert Dual EC DRBG removal commit as it was not accepted for 2.0.7
version of the module.

This reverts commit 200f249b.

(cherry picked from commit 1a9d60d2)

(cherry picked from commit 964eaad7)

some versions of Windows.

tarball some don't exist) so set TEST='' to avoid linking to them. This also
avoids problems on platforms that copy instead of symlink.

machines.

entropy source fails.