add infrastructure to record and report the version of libc.so

this is still experimental and subject to change. for git checkouts,
an attempt is made to record the exact revision to aid in bug reports
and debugging. no version information is recorded in the static libc.a
or binaries it's linked into.

tools/version.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+if test -d .git ; then
+if type git >/dev/null 2>&1 ; then
+git describe --tags --match 'v[0-9]*' 2>/dev/null \
+| sed -e 's/^v//' -e 's/-/-git-/'
+else
+sed 's/$/-git/' < VERSION
+fi
+else
+cat VERSION
+fi