Just built current CVS through with GCC 4.0.2 on Cygwin. It might be imagination, but it seems significantly quicker that 4.0.
VC++ 2003 also builds through,
and I've GCC 3.3 on Darwin going at the moment as does GCC 3.3 on Darwin, with the exception of the XPath tests. There are conflicting assert macros I think - probably just need to juggle some paths.