Fixed that annoying ar warning about -u being ignored.

config/linux-gnulibc1

@@ -30,6 +30,11 @@ if test -z "$CC"; then
     fi
 fi
 
+# Set flags for gnu ar (apparently via libtool, so AR_FLAGS, not ARFLAGS)
+# If you don't do this, you will get warnings about the 'u' in
+# automake's default 'cru' args.
+AR_FLAGS=crD
+
 # Figure out GNU C compiler flags
 . $srcdir/config/gnu-flags