util/mk1mf.pl: use LINK_CMD instead of LINK variable.

Trouble is that LINK variable assignment in make-file interferes with
LINK environment variable, which can be used to modify Microsoft's
LINK.EXE behaviour.

RT#4289

Reviewed-by: Richard Levitte <levitte@openssl.org>
(cherry picked from commit d44bb1c3)

Resolved conflicts:
	util/pl/VC-32.pl

(cherry picked from commit 0fffd522)