luajit: Disable for MIPS architecture with soft-float

Currently luajit is not supported on MIPS soft-float userlands. Upstream
plans to support it in the future:

   http://wiki.luajit.org/Open-Sponsorships#MIPS-Soft-Float-and-Dual-Number-Port

Fixes:

   http://autobuild.buildroot.net/results/d52/d5232a215e9e9aeb40b2e4e353329a27603c79ab/

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
luajit: needs for 32bit archictectures a 32bit host gcc

For 32 bit archictectures the luajit package needs a host compiler
able to generate 32 bit code using the "-m32" option so check if that
option is supported.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: François Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
luajit: add host variant
luainterpreter: add host variant
luarocks: allow to work with host-luainterpreter

when we embed luajit on target, we use luarocks with host-luajit instead of host-lua
lua-iconv: new package