Patch for 96948

[Martin Storsjö]

Hi,

On Mon, 7 Sep 2020, Kirill Müller via Gcc-patches wrote:

> As requested, attaching a patch for 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96948. This solves a problem 
> with _Unwind_Backtrace() on mingw64 + SEH.

What a coincidence - I actually sent a patch for the exact same thing 
last week, see 
https://gcc.gnu.org/pipermail/gcc-patches/2020-September/553082.html.

My version doesn't set gcc_context.cfa though, but is simpler by avoiding 
the whole "first" flag logic.

I can send an updated patch that also sets gcc_context.cfa in a smilar 
manner to the previous one.

// Martin