Merge pull request #1470 from compnerd/1447

lldb: repair the Windows build after #1447

Author: compnerd

lldb/include/lldb/Symbol/SwiftASTContext.h

@@ -48,7 +48,7 @@ class IRGenOptions;
 class NominalTypeDecl;
 class SearchPathOptions;
 class SILModule;
-class TBDGenOptions;
+struct TBDGenOptions;
 class VarDecl;
 class ModuleDecl;
 class SourceFile;