[weak vtables] Place class definitions into anonymous namespaces to prevent weak vtables.

This patch places class definitions in implementation files into anonymous
namespaces to prevent weak vtables. This eliminates the need of providing an
out-of-line definition to pin the vtable explicitly to the file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195092 91177308-0d34-0410-b5e6-96231b3b80d8

examples/Kaleidoscope/Chapter6/toy.cpp

@@ -101,17 +101,14 @@ static int gettok() {
 //===----------------------------------------------------------------------===//
 // Abstract Syntax Tree (aka Parse Tree)
 //===----------------------------------------------------------------------===//
-
+namespace {
 /// ExprAST - Base class for all expression nodes.
 class ExprAST {
 public:
-  virtual ~ExprAST();
+  virtual ~ExprAST() {}
   virtual Value *Codegen() = 0;
 };
 
-// Provide out-of-line definition to prevent weak vtable.
-ExprAST::~ExprAST() {}
-
 /// NumberExprAST - Expression class for numeric literals like "1.0".
 class NumberExprAST : public ExprAST {
   double Val;
@@ -214,6 +211,7 @@ public:
   
   Function *Codegen();
 };
+} // end anonymous namespace
 
 //===----------------------------------------------------------------------===//
 // Parser