[gn build] Port 30bb0c4

Author: llvmgnsyncbot

llvm/utils/gn/secondary/lldb/tools/lldb-dap/BUILD.gn

@@ -43,6 +43,7 @@ executable("lldb-dap") {
     "Breakpoint.cpp",
     "BreakpointBase.cpp",
     "DAP.cpp",
+    "DAPError.cpp",
     "DAPLog.cpp",
     "EventHelper.cpp",
     "ExceptionBreakpoint.cpp",