add package LuaJIT

LuaJIT compilation has 2 steps:

 - buildvm is compiled (src/host/buildvm.c)
 - buildvm generates object code of LuaJIT itself.

Pointer size of buildvm should be the same of target system (Windows), which is now 32 in MXE, as far as I know. HOST_CC="gcc -m32" tells build system to compile 32-bit buildvm. Buildvm is used only while compilation and is not distributed.