[DebugInfo] Make AsmPrinter struct HandlerInfo and Handlers protected

[yonghong-song]

Summary

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 <[e-mail]>

[yonghong-song]

@echristo @aprantl @dblaikie
This patch and two other patches (D55755, D55752) implemented a different mechanism
to generate BTF than patch D53736. D53736 has its most implementation under
lib/CodeGen/AsmPrinter. The new mechanism put most implementation under BTF target.

(1) https://reviews.llvm.org/D55755, moving header files
(2) https://reviews.llvm.org/D55756, changes some fields from private to protected
(3) https://reviews.llvm.org/D55752, changes only under target BPF

It will be good if you can help review all related patches and provide your opinions soon.
Thanks! Real appreciated.

[echristo]

Thanks for the split. LGTM!

-eric

llvm/trunk/include/llvm/CodeGen/AsmPrinter.h

private:
   // The garbage collection metadata printer table.
   void *GCMetadataPrinters = nullptr; // Really a DenseMap.
 
   /// Emit comments in assembly output if this is true.
   bool VerboseAsm;
 
   static char ID;
 
+protected:
+  /// Protected struct HandlerInfo and Handlers permit target extended
+  /// AsmPrinter adds their own handlers.
   struct HandlerInfo {
     AsmPrinterHandler *Handler;
     const char *TimerName;
     const char *TimerDescription;
     const char *TimerGroupName;
     const char *TimerGroupDescription;
 
     HandlerInfo(AsmPrinterHandler *Handler, const char *TimerName,