Remove multiple use of weak_import attribute on
same declaration. Templatize dropAttr for general use.

llvm-svn: 133724
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 487390b..4a000e9 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2046,7 +2046,7 @@
     Diag(New->getLocation(), diag::warn_weak_import) << New->getDeclName();
     Diag(Old->getLocation(), diag::note_previous_definition);
     // Remove weak_import attribute on new declaration.
-    New->dropWeakImportAttr();
+    New->dropAttr<WeakImportAttr>();
   }
 
   // Merge the types.