Deterministic builds / ar warns about u modifier
Building Tor from source brings up this warning several times:
u' modifier ignored sinceD' is the default (see `U')" a lot.
The fix is to change the according line in Makefile.in to
(easy to find with
grep -n "ARFLAGS =" Makefile.in)
Since Makefile.in is created by the
./configure script, the default flags need to be changed:
"ARFLAGS will default to cru; you can override this variable by setting it in your Makefile.am or by AC_SUBSTing it from your configure.ac."
binutils upstream provides a configure option '--enable-deterministic-archives', which makes this behaviour the default, though it can still be disabled at runtime via the 'u' switch, in case someone wants to use ar to pack non-library files in an archive and cares about the metadata.