[DebugInfo] Make AsmPrinter struct HandlerInfo and Handlers protected

In AsmPrinter, make struct HandlerInfo and SmallVector
Handlers protected, so target extended AsmPrinter will
be able to add their own handlers.

Signed-off-by: Yonghong Song <yhs@fb.com>

Differential Revision: https://reviews.llvm.org/D55756

llvm-svn: 349602

llvm/include/llvm/CodeGen/AsmPrinter.h

@@ -138,6 +138,9 @@ private:
 
   static char ID;
 
+protected:
+  /// Protected struct HandlerInfo and Handlers permit target extended
+  /// AsmPrinter adds their own handlers.
   struct HandlerInfo {
     AsmPrinterHandler *Handler;
     const char *TimerName;