Do not use 'u' flag for ar

The Reproducible Builds effort (https://wiki.debian.org/ReproducibleBuilds) in Debian (at least) means that 'ar' is built in deterministic mode as default: all timestamps are set to 0.

This is not compatible with the use of the 'u' flag, and therefore ARFLAGS has to be changed from 'cru' to 'cr'.

This gets rid of the harmless but annoying warning
  ar: `u' modifier ignored since `D' is the default (see `U')

diff --git a/configure.ac b/configure.ac
index 0b7a64bad40376ebdf7bd30eb1accb3969a73b6c..3d88a08fb03809835457cfb2b659efc6e17a0a0a 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -74,6 +74,9 @@ AM_PATH_PYTHON
 # Tools for creating libraries (note that we do not use libtool)
 m4_ifdef([AM_PROG_AR], [AM_PROG_AR]) dnl AM_PROG_AR requires automake 1.12
 AC_PROG_RANLIB
+dnl Recent debian/ubuntu (at least) have built 'ar' so that deterministic mode is the default.
+dnl This means that it does not make sense to use the 'u' flag (default ARFLAGS is 'cru').
+AC_SUBST([ARFLAGS], [cr])
 
 ### Check for a C++ compiler
 dnl We have to do weird tricks so that autoconf does not touch CXXFLAGS even