ar rcu

[Hugo Musso Gualandi <hgualandi@...>]

When I compile Lua 5.4.4 on Debian 11 or Ubuntu 20.04, it gives a 
compilation warning in the "ar" step:

   ar: `u' modifier ignored since `D' is the default (see `U')

This was previously reported to this list by Egor Skriptunoff here [1], 
for Lua 5.4.0. The cause of the problem is the "ar rcu" in the 
Makefile. It is only in the final Lua release. In the git 
repository[2], it uses "ar rc" and doesn't have this warning.

I believe it should be safe to use "ar rc" instead. Hopefully the Unix 
wizards on this list can clarify this... My understanding is that the 
"u" flag is only supposed to help reduce the compilation time a little 
bit when re-compiling the project. However, it comes at the cost of 
embedding timestamps into the library file, which makes the resulting 
build non-deterministic. For this reason, Debian started ignoring this 
option and complains when it is used.

[1] http://lua-users.org/lists/lua-l/2018-09/msg00280.html
[2] 
https://github.com/lua/lua/blob/8426d9b4d4df1da3c5b2d759e509ae1c50a86667/makefile#L76

-- Hugo