Fix a thinko that caused us not to compute __builtin_offset as a
constant expression in C. 

llvm-svn: 102762
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 8252611..00662a5 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1943,7 +1943,6 @@
     case UnaryOperator::AddrOf:
     case UnaryOperator::Deref:
       return ICEDiag(2, E->getLocStart());
-    case UnaryOperator::OffsetOf:
     case UnaryOperator::Extension:
     case UnaryOperator::LNot:
     case UnaryOperator::Plus:
@@ -1952,7 +1951,11 @@
     case UnaryOperator::Real:
     case UnaryOperator::Imag:
       return CheckICE(Exp->getSubExpr(), Ctx);
+    case UnaryOperator::OffsetOf:
+      break;
     }
+    
+    // OffsetOf falls through here.
   }
   case Expr::OffsetOfExprClass: {
       // Note that per C99, offsetof must be an ICE. And AFAIK, using