[gn build] Port 6c4febe

Author: llvmgnsyncbot

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

@@ -31,6 +31,7 @@ static_library("Host") {
     "common/LZMA.cpp",
     "common/LockFileBase.cpp",
     "common/MainLoopBase.cpp",
+    "common/MemoryMonitor.cpp",
     "common/MonitoringProcessLauncher.cpp",
     "common/NativeProcessProtocol.cpp",
     "common/NativeRegisterContext.cpp",