Meta: Add the start of a gn build based on the LLVM gn build

"based on" in this context means "largely copied from"

Meta/gn/secondary/Userland/Libraries/LibCore/BUILD.gn

@@ -0,0 +1,142 @@
+source_set("sources") {
+  include_dirs = [ "//Userland/Libraries" ]
+  deps = [ "//AK" ]
+  sources = [
+    "AnonymousBuffer.cpp",
+    "AnonymousBuffer.h",
+    "ArgsParser.cpp",
+    "ArgsParser.h",
+    "Command.cpp",
+    "Command.h",
+    "ConfigFile.cpp",
+    "ConfigFile.h",
+    "DateTime.cpp",
+    "DateTime.h",
+    "Debounce.h",
+    "DeferredInvocationContext.h",
+    "DirIterator.cpp",
+    "DirIterator.h",
+    "Directory.cpp",
+    "Directory.h",
+    "DirectoryEntry.cpp",
+    "DirectoryEntry.h",
+    "ElapsedTimer.cpp",
+    "ElapsedTimer.h",
+    "Event.cpp",
+    "Event.h",
+    "EventLoop.cpp",
+    "EventLoop.h",
+    "EventLoopImplementation.cpp",
+    "EventLoopImplementation.h",
+    "EventLoopImplementationUnix.cpp",
+    "EventLoopImplementationUnix.h",
+    "File.cpp",
+    "File.h",
+    "Forward.h",
+    "LockFile.cpp",
+    "LockFile.h",
+    "MappedFile.cpp",
+    "MappedFile.h",
+    "MimeData.cpp",
+    "MimeData.h",
+    "NetworkJob.cpp",
+    "NetworkJob.h",
+    "NetworkResponse.h",
+    "Notifier.cpp",
+    "Notifier.h",
+    "Object.cpp",
+    "Object.h",
+    "Process.cpp",
+    "Process.h",
+    "ProcessStatisticsReader.cpp",
+    "ProcessStatisticsReader.h",
+    "Promise.h",
+    "Property.cpp",
+    "Property.h",
+    "Proxy.h",
+    "SOCKSProxyClient.cpp",
+    "SOCKSProxyClient.h",
+    "SecretString.cpp",
+    "SecretString.h",
+    "SessionManagement.cpp",
+    "SessionManagement.h",
+    "SharedCircularQueue.h",
+    "Socket.cpp",
+    "Socket.h",
+    "SocketAddress.h",
+    "StandardPaths.cpp",
+    "StandardPaths.h",
+    "System.cpp",
+    "System.h",
+    "SystemServerTakeover.cpp",
+    "SystemServerTakeover.h",
+    "TCPServer.cpp",
+    "TCPServer.h",
+    "ThreadEventQueue.cpp",
+    "ThreadEventQueue.h",
+    "Timer.cpp",
+    "Timer.h",
+    "UDPServer.cpp",
+    "UDPServer.h",
+    "UmaskScope.h",
+    "Version.cpp",
+    "Version.h",
+  ]
+  if (current_os != "android") {
+    sources += [
+      "Account.cpp",
+      "Account.h",
+      "FilePermissionsMask.cpp",
+      "FilePermissionsMask.h",
+      "GetPassword.cpp",
+      "GetPassword.h",
+      "Group.cpp",
+      "Group.h",
+      "LocalServer.cpp",
+      "LocalServer.h",
+    ]
+  }
+}
+
+source_set("filewatcher") {
+  include_dirs = [ "//Userland/Libraries" ]
+  sources = [ "FileWatcher.h" ]
+  deps = [ "//AK" ]
+  frameworks = []
+  if (current_os == "linux") {
+    sources += [ "FileWatcherLinux.cpp" ]
+  } else if (current_os == "mac") {
+    sources += [ "FileWatcherMacOS.mm" ]
+    frameworks += [
+      "CoreFoundation.framework",
+      "CoreServices.framework",
+      "Foundation.framework",
+    ]
+  } else if (current_os == "serenity") {
+    sources += [ "FileWatcherSerenity.cpp" ]
+  } else {
+    sources += [ "FileWatcherUnimplemented.cpp" ]
+  }
+}
+
+shared_library("LibCore") {
+  libs = []
+
+  if (current_os == "linux" || current_os == "android") {
+    libs += [ "dl" ]
+  }
+  if (current_os == "linux") {
+    libs += [ "rt" ]
+  }
+
+  output_name = "core"
+
+  deps = [
+    ":filewatcher",
+    ":sources",
+    "//AK:sources",
+    "//Meta/gn/build/libs/crypt",
+    "//Meta/gn/build/libs/pthread",
+    "//Userland/Libraries/LibSystem",
+  ]
+}