Downgrade the "declaration does not declare anything" error to a
warning. It's not harmful to have such pointless declarations, and GCC
does not diagnose this issue consistently.

llvm-svn: 100814
diff --git a/clang/test/SemaCXX/class.cpp b/clang/test/SemaCXX/class.cpp
index 508ca4d..7eea67a 100644
--- a/clang/test/SemaCXX/class.cpp
+++ b/clang/test/SemaCXX/class.cpp
@@ -103,7 +103,7 @@
 
   // PR3020: This used to crash due to double ownership of C4.
   struct C4;
-  C4; // expected-error {{declaration does not declare anything}}
+  C4; // expected-warning {{declaration does not declare anything}}
 }
 
 struct C4 {