Add tool to obtain architectures of a program.

This is used to build a program with the same architecture(s) as
a specified program (default /usr/bin/true).

tools/binarchs.sh

+#! /bin/bash
+
+# Get architectures for system programs.
+# NOTE: Currently needed to build 'which' on 10.4.
+
+REFPROG="${1:-/usr/bin/true}"
+
+ARCHS="$(file $REFPROG | grep ' executable ' | sed 's|.* executable ||')"
+ARCHFLAGS="$(for a in $ARCHS; do echo -n ' -arch' $a; done)"
+
+echo $ARCHFLAGS