fix(build): distinguish vim.mpack from global require'mpack'

problem: the api of vim.mpack is not compatible with a system provided mpack
solution: don't require 'mpack' directly from the system path

src/nvim/generators/preload.lua

@@ -4,6 +4,7 @@ package.path = srcdir .. '/src/nvim/?.lua;' ..srcdir .. '/runtime/lua/?.lua;' ..
 _G.vim = require'vim.shared'
 _G.vim.inspect = require 'vim.inspect'
 package.cpath = package.cpath .. ';' .. nlualib
+require 'nlua0'
 
 arg[0] = table.remove(arg, 1)
 return loadfile(arg[0])()