Following up to myself:

On Thu, Apr 02, 2009 at 10:51:11PM +0100, Jeremy Henty  wrote:
> 
> I  note that  (a) SCons.Environment.Append  has a  lot  of different
> cases depending on  the types of things, and (b)  the bug appears to
> strike CCFLAGS but  not CPPPATH or CPPFLAGS.  Maybe  the CCFLAGS key
> is associated to a value of a different type?

And indeed it is!  CPPPATH and  CPPFLAGS map to lists but CCFLAGS amps
to a CLVar,  which is derived from UserList.   The CCFLAGS value wraps
an ordinary list.   Append("-DLINUX") splits "-DLINUX" into characters
and appends those characters to wrapped list.  Even more interesting:

    $ python
    Python 2.6.1 (r261:67515, Dec  9 2008, 10:18:43)
    [GCC 4.1.2] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import UserList
    >>> UserList.UserList([]) + 'adgsdf'
    ['a', 'd', 'g', 's', 'd', 'f']
    >>>

Clearly SCons.Environment.Append()  has started doing  the wrong thing
when  the value  to  append to  is  a UserList.   Either UserList  has
changed in  Python 2.6 or something  else has changed  that breaks the
internal  logic of  SCons.Environment.Append().  What  does  the above
Python code do under Python 2.5?

Regards,

Jeremy Henty