IRGen: adjust the replacemnts section for Windows

Group the section for the replacements on PE/COFF.  The group is needed
to ensure that we are able to order the marker for the start and stop
properly.  Without the grouping there is no way to guarantee the
ordering.

Author: compnerd

lib/IRGen/GenDecl.cpp

@@ -1233,7 +1233,7 @@ static std::string getDynamicReplacementSection(IRGenModule &IGM) {
     sectionName = "swift5_replace";
     break;
   case llvm::Triple::COFF:
-    sectionName = ".sw5repl";
+    sectionName = ".sw5repl$B";
     break;
   default:
     llvm_unreachable("Don't know how to emit field records table for "