[gn build] Port 57c66b3

Author: llvmgnsyncbot

llvm/utils/gn/secondary/lldb/source/Breakpoint/BUILD.gn

@@ -34,6 +34,7 @@ static_library("Breakpoint") {
     "StoppointCallbackContext.cpp",
     "StoppointSite.cpp",
     "Watchpoint.cpp",
+    "WatchpointAlgorithms.cpp",
     "WatchpointList.cpp",
     "WatchpointOptions.cpp",
     "WatchpointResource.cpp",