Add a constructor for BuildVectorSDNode and revert the temporary workaround

from 66280.  I was unable to verify this with gcc-3.4.6, but with gcc-3.3 it
avoids the "base class with only non-default constructor in class without
a constructor" warning.  Apparently that warning was promoted to an error
in gcc-3.4.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66424 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/SelectionDAGNodes.h

@@ -1114,10 +1114,6 @@ private:
   friend struct ilist_traits<SDNode>;
 
 public:
-  
-  /// Default SDNode constructor.
-  SDNode() {}
-    
   //===--------------------------------------------------------------------===//
   //  Accessors
   //
@@ -1936,6 +1932,8 @@ public:
 /// BuildVectorSDNode - A "pseudo-class" with methods for operating on
 /// BUILD_VECTORs.
 class BuildVectorSDNode : public SDNode {
+  // These are constructed as SDNodes and then cast to BuildVectorSDNodes.
+  explicit BuildVectorSDNode();        // Do not implement
 public:
   /// isConstantSplat - Check if this is a constant splat, and if so, find the
   /// smallest element size that splats the vector.  If MinSplatBits is