MSVC: allow linking with the cURL library

Teach the clink.pl script that -lcurl is a request to link with the
cURL library, and drop NO_CURL from config.mak.uname for the MSVC
platform.

Signed-off-by: Marat Radchenko <marat@slonopotamus.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>