1. Move HOSTCC/HOSTLD to nmk (note there are rules in nmk
   that make use of these variables already)

2. Make CC/LD derive from HOSTCC/HOSTLD

Note that one can still change anything from the command line.

travis-ci: success for build system: make CC/LD derive from HOSTCC/HOSTLD
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>