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

llvm-svn: 317703
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 29b1441..9a23e61 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -290,7 +290,7 @@
   case MCFragment::FT_Padding:
     return cast<MCPaddingFragment>(F).getSize();
 
-  case MCFragment::FT_SafeSEH:
+  case MCFragment::FT_SymbolId:
     return 4;
 
   case MCFragment::FT_Align: {
@@ -563,8 +563,8 @@
     break;
   }
 
-  case MCFragment::FT_SafeSEH: {
-    const MCSafeSEHFragment &SF = cast<MCSafeSEHFragment>(F);
+  case MCFragment::FT_SymbolId: {
+    const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
     OW->write32(SF.getSymbol()->getIndex());
     break;
   }