[WinEH] Set NoModuleLevelChanges in clone flags

Summary:
This is necessary to keep the cloner from making bogus copies of debug
metadata attached to the IR it is cloning.
Also, avoid running RemapInstruction over all instructions in the common
case that no cloning was performed.

Reviewers: rnk, andrew.w.kaylor, majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13514

llvm-svn: 249591