EH on cygwin - sjlj or frame unwinding model?

[Billinghurst, David (CRTS)]

There are exception handling problems with gcc-3.0 - See PR 3099.  I have
had a poke around, but am waaay out of my depth.

If I configure with --enable-sjlj-exceptions I seem to get reasonable
testsuite results.

		=== g++ Summary ===

# of expected passes		6439
# of unexpected failures	15
# of unexpected successes	4
# of expected failures		101
# of unresolved testcases	1
# of untested testcases		15


Some questions/comments:

Which exception handling model can/should we use on cygwin?  (At this stage,
I guess the one that works)

If we are going to use sjlj exceptions, can we make it the default for
cygwin?  If so, how?  Should it be documented in the platform specific
notes?

Shouldn't we document  --enable-sjlj-exceptions in the top level
installation instructions http://gcc.gnu.org/install/index.html ?

If I understand the libstdc++-v3 configuration process, the exception
handling model is determined from g++.  If so, the mention of
--enable-sjlj-exceptions in the libstdc++-v3 configuration docs
http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html is wrong, incomplete
or in the wrong place.