Makefile: honor NO_CURL when setting REMOTE_CURL_* variables

Makefile: honor NO_CURL when setting REMOTE_CURL_* variables

Previously, these variables were set before there was a chance to set
NO_CURL.

This made a difference only during 'make install', because by installing
$(REMOTE_CURL_ALIASES), the rule  tries to access $(REMOTE_CURL_PRIMARY),
which was never installed. On Windows, this fails; on Unix, stale symbolic
links are created.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Acked-by: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>