[Reproducers] Flush files to disk periodically

Periodically flush some of the data to disk. Although not perfect, this
helps when the debugger crashes.

llvm-svn: 360286

lldb/include/lldb/Utility/Reproducer.h

@@ -126,6 +126,7 @@ public:
     m_os << t;
     if (newline)
       m_os << '\n';
+    m_os.flush();
   }
 
   const FileSpec &GetFilename() { return m_filename; }

lldb/include/lldb/Utility/ReproducerInstrumentation.h

@@ -542,7 +542,9 @@ public:
     SerializeAll(tail...);
   }
 
-  void SerializeAll() {}
+  void SerializeAll() {
+    m_stream.flush();
+  }
 
 private:
   /// Serialize pointers. We need to differentiate between pointers to