windows: Windows-friendly segfault handling
windows: Windows-friendly segfault handling

We could do better by being more Windows-specific, probably most easily
by using _set_se_translator() to get the access violation early and
grabbing the address from the argument, etc.  But this patch at least
compiles and should generate stack traces in --debug mode on Windows.

The same code could be used on other platforms which don't support
sigaction(), if we run into any.

Plasmaworks/Rogue,AbePralle/Rogue,AbePralle/Rogue,Plasmaworks/Rogue,Plasmaworks/Rogue,Plasmaworks/Rogue