[Bug target/77333] Incorrect stack adjust in epilogue when targeting i686-w64-mingw32

[tony at kelman dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77333

--- Comment #14 from Tony Kelman <tony at kelman dot net> ---
I'll look into whether the same flag changes the behavior in the same way on
gcc 5.

Using the opensuse repo's current cross compiler version, I reduced
SLPVectorizer.cpp down to the attached version. It's maybe so small that
there's UB making it useless to look at, but replacing SLPVectorizer.cpp with
this copy reproduces the known-good behavior with -fno-ipa-cp and the segfault
without.