[lldb] [gdb-remote server] Introduce new stop reasons for fork and vfork

Introduce three new stop reasons for fork, vfork and vforkdone events.
This includes server support for serializing fork/vfork events into
gdb-remote protocol.  The stop infos for the two base events take a pair
of PID and TID for the newly forked process.

Differential Revision: https://reviews.llvm.org/D100196

lldb/source/API/SBThread.cpp

@@ -173,6 +173,7 @@ size_t SBThread::GetStopReasonDataCount() {
         case eStopReasonThreadExiting:
         case eStopReasonInstrumentation:
         case eStopReasonProcessorTrace:
+        case eStopReasonVForkDone:
           // There is no data for these stop reasons.
           return 0;
 
@@ -195,6 +196,12 @@ size_t SBThread::GetStopReasonDataCount() {
 
         case eStopReasonException:
           return 1;
+
+        case eStopReasonFork:
+          return 1;
+
+        case eStopReasonVFork:
+          return 1;
         }
       }
     }
@@ -225,6 +232,7 @@ uint64_t SBThread::GetStopReasonDataAtIndex(uint32_t idx) {
         case eStopReasonThreadExiting:
         case eStopReasonInstrumentation:
         case eStopReasonProcessorTrace:
+        case eStopReasonVForkDone:
           // There is no data for these stop reasons.
           return 0;
 
@@ -258,6 +266,12 @@ uint64_t SBThread::GetStopReasonDataAtIndex(uint32_t idx) {
 
         case eStopReasonException:
           return stop_info_sp->GetValue();
+
+        case eStopReasonFork:
+          return stop_info_sp->GetValue();
+
+        case eStopReasonVFork:
+          return stop_info_sp->GetValue();
         }
       }
     }