Be more careful about deciding which filemap implementation to use for xmlwf.  Part of SF patch #465018.
Be more careful about deciding which filemap implementation to use for
xmlwf.  Part of SF patch #465018.

Only add the -fexceptions option when the version of GCC we're using
actually supports it.  This relates to & partially solves SF bug #445893;
see also SF bug #419585 for why the option was originally added.

cgwalters/expat-git-mirror,cgwalters/expat-git-mirror,cgwalters/expat-git-mirror