[gn build] Port 2d30a60

Author: llvmgnsyncbot

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

@@ -51,6 +51,7 @@ executable("lldb-dap") {
     "FunctionBreakpoint.cpp",
     "Handler/AttachRequestHandler.cpp",
     "Handler/BreakpointLocationsHandler.cpp",
+    "Handler/CancelRequestHandler.cpp",
     "Handler/CompileUnitsRequestHandler.cpp",
     "Handler/CompletionsHandler.cpp",
     "Handler/ConfigurationDoneRequestHandler.cpp",