[Windows SEH]: Fix -O2 crash for Windows -EHa

This patch fixes a Windows -EHa crash induced by previous commit 797ad701.
The crash was caused by "LifetimeMarker" scope (with option -O2) that should not be considered as SEH Scope.

This change also turns off -fasync-exceptions by default under -EHa option for now.

Differential Revision: https://reviews.llvm.org/D103664#2799944