LuaRocks site_config misses some lines

[mpeterv]

LuaRocks may add some lines to site_config.lua, like this:

if [ -n "$(MULTIARCH_SUBDIR)" ] ;\
then \
   echo 'site_config.LUAROCKS_EXTERNAL_DEPS_SUBDIRS={ bin="bin", lib={ "lib", [[$(MULTIARCH_SUBDIR)]] }, include="include" }' >> src/luarocks/site_config.lua ;\
   echo 'site_config.LUAROCKS_RUNTIME_EXTERNAL_DEPS_SUBDIRS={ bin="bin", lib={ "lib", [[$(MULTIARCH_SUBDIR)]] }, include="include" }' >> src/luarocks/site_config.lua ;\
fi

Where $MULTIARCH_SUBDIR) is set as follows:

if [ "$LUAROCKS_UNAME_S" = Linux ]
then
   GCC_ARCH=`gcc -print-multiarch 2>/dev/null`
   if [ -n "$GCC_ARCH" -a -d "/usr/lib/$GCC_ARCH" ]
   then
      MULTIARCH_SUBDIR="lib/$GCC_ARCH"
   elif [ -d "/usr/lib64" ]
   then
      # Useful for Fedora systems
      MULTIARCH_SUBDIR="lib64"
   fi
fi

($LUAROCKS_UNAME_S is uname -s)

These lines are not in site_config.lua installed by torch/distro: https://github.com/torch/luajit-rocks/blob/411f4b9d9c4be176d4aab965ebfce50911583e14/luarocks/src/luarocks/site_config.lua.in

This affects ease of linking Lua rocks with libraries installed e.g. in /usr/lib/x86_64-linux-gnu, see daurnimator/lua-http#39 (comment)

[d9k]

@andresy, still an issue

site_config.LUAROCKS_EXTERNAL_DEPS_SUBDIRS and site_config.LUAROCKS_RUNTIME_EXTERNAL_DEPS_SUBDIRS are missing at site_config.lua