NFC:  Rename MCSafeSEHFragment to MCSymbolIdFragment

Summary:
This fragment emits a symbol ID and will be useful for more than just Safe SEH
tables (e.g., I plan to re-use it for Control Flow Guard tables).  This is
simply a rename refactor.

Reviewers: rnk

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D39770

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317703 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed