Hello libtool devs,

There's a common information/warning message that occurs with building secp256k1 for example where it states:

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

This can be resolved if "cru" is changed to "crU" in:

/usr/share/aclocal/libtool.m4

Please consider doing this, thank you !