luarocks: prefers a hardcoded interpreter

Since there is a need to use the tarantool interpreter instead of lua,
a couple of changes were made to apply the FORCE_HARDCODED flag,
which allows you to use tarantool as an interpreter even if
there is a luarocks config.

Author: Japsty

src/luarocks/cmd.lua

@@ -573,6 +573,9 @@ function cmd.run_command(description, commands, external_namespace, ...)
    -- Now that the config is fully loaded, reinitialize fs using the full
    -- feature set.
    fs.init()
+   if cfg.variables.FORCE_HARDCODED and cfg.variables.LUA_INTERPRETER then
+      lua_found = true
+   end
 
    -- if the Lua interpreter wasn't explicitly found before cfg.init,
    -- try again now.

src/luarocks/core/cfg.lua

@@ -763,6 +763,10 @@ function cfg.init(detected, warning)
       end
    end
 
+   if hardcoded.FORCE_HARDCODED then
+      util.deep_merge(cfg.variables, hardcoded)
+   end
+
    ----------------------------------------
    -- Config files are loaded.
    -- Let's finish up the cfg table.