Getting srcdir in script executed using m4_esyscmd in AC_INIT

[Bob Friesenhahn <bfriesen@xxxxxxxxxxxxxxxxxxx>]

I am trying to update the Autoconf and Automake initializations in 
GraphicsMagick to the current standard.  There is an external script 
which produces all of the version information.  This script needs to 
access a file (called ChangeLog) in the top of the source directory.

I am using this syntax in configure.ac:

AC_INIT(m4_esyscmd([./version.sh packagename]),
        m4_esyscmd([./version.sh packageversion]),
        m4_esyscmd([./version.sh packagebugreport]))

This works fine when building in the source directory.

The problem I am encountering is that in the context of AC_INIT and 
m4_esyscmd, I do not know how to obtain the path to the top of the 
source directory.

Can someone please give me a clue as to how to determine the top of 
the source directory?

Thanks,

Bob
--
Bob Friesenhahn
bfriesen@xxxxxxxxxxxxxxxxxxx, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
Public Key,     http://www.simplesystems.org/users/bfriesen/public-key.txt