exception handling poll

[John Carr]

>   Assuming the .eh_frame section is completely read-only, at what
>   eh/text ratio would you find it acceptible that that information
>   is always there?
> 
> Can you live with 10%?  8?  5?  3?

Probably 3%.

For the first egcs release we should:

1. Default C -fexceptions off on all targets.  Not one extra bit for
exception handling.

2. Get the overhead for code not using exceptions, but compiled with
exceptions enabled, under 8% (for "typical" code, whatever that is).
If that means setjmp exceptions on x86, then we do that.

3. Document and warn that the next egcs release will be binary
incompatible if exceptions are used.

Then we have a few months to fix exceptions and we can look at making
them better, smaller, faster, or compatible with the system compiler
without delaying a release.