Fix lua-Spore build when cross-compiling...
Fix lua-Spore build when cross-compiling...

Luarocks builtin build-modules enforces -I & -L flags set to LUA_INCDIR
& LUA_LIBDIR, respecitvely. If they're not overriden, they default to
the host's paths. Depending on the exact TC, this may prevent the linker
to do its job properly, because it'll barf on libraries targeting a
different architecture...

(Affected the lpeg depbuild)

Hzj-jie/koreader-base,apletnev/koreader-base,Frenzie/koreader-base,Frenzie/koreader-base,frankyifei/koreader-base,NiLuJe/koreader-base,houqp/koreader-base,apletnev/koreader-base,NiLuJe/koreader-base,frankyifei/koreader-base,Hzj-jie/koreader-base,Hzj-jie/koreader-base,apletnev/koreader-base,houqp/koreader-base,frankyifei/koreader-base,Hzj-jie/koreader-base,NiLuJe/koreader-base,Frenzie/koreader-base,koreader/koreader-base,houqp/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,apletnev/koreader-base,Frenzie/koreader-base,koreader/koreader-base,frankyifei/koreader-base,koreader/koreader-base,houqp/koreader-base