[gn build] Port 3986cff

Author: llvmgnsyncbot

llvm/utils/gn/secondary/lldb/source/Plugins/Process/Utility/BUILD.gn

@@ -35,6 +35,7 @@ static_library("Utility") {
     "NativeRegisterContextDBReg_x86.cpp",
     "NativeRegisterContextRegisterInfo.cpp",
     "NetBSDSignals.cpp",
+    "OpenBSDSignals.cpp",
     "RegisterContextDarwin_arm.cpp",
     "RegisterContextDarwin_arm64.cpp",
     "RegisterContextDarwin_i386.cpp",