[SLPVectorizer] Don't insert an extractelement before a catchswitch

A catchswitch cannot be preceded by another instruction in the same
basic block (other than a PHI node).

Instead, insert the extract element right after the materialization of
the vectorized value.  This isn't optimal but is a reasonable compromise
given the constraints of WinEH.

This fixes PR27163.

llvm-svn: 265157