how to AC_DEFINE* a fully evaluated variable?

[mcmahill]

I tried something like this in my configure.ac file:

MYDIR=${datadir}/foo
AC_DEFINE_UNQUOTED(MYDIR,"$MYDIR",[default search directory for foo])

but this ends up with:

/* default search directory for foo */
#define MYDIR "${prefix}/share/foo"

in config.h but what I really wanted is the fully expanded directory, like
"/opt/something/share/foo"  or "/usr/local/share/foo"


Is there an option which will fully expand a variable or do I need to do
something like

CPPFLAGS="$CPPFLAGS -DMYDIR=$MYDIR"

instead?

Thanks
-Dan