LibCore+LibSystem: Move syscall wrappers from LibSystem to LibCore

With this change, System::foo() becomes Core::System::foo().

Since LibCore builds on other systems than SerenityOS, we now have to
make sure that wrappers work with just a standard C library underneath.

Userland/Utilities/js.cpp

@@ -13,6 +13,7 @@
 #include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
 #include <LibCore/StandardPaths.h>
+#include <LibCore/System.h>
 #include <LibJS/AST.h>
 #include <LibJS/Bytecode/BasicBlock.h>
 #include <LibJS/Bytecode/Generator.h>
@@ -61,7 +62,6 @@
 #include <LibJS/Runtime/Value.h>
 #include <LibLine/Editor.h>
 #include <LibMain/Main.h>
-#include <LibSystem/Wrappers.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <stdio.h>
@@ -1107,7 +1107,7 @@ public:
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
 #ifdef __serenity__
-    TRY(System::pledge("stdio rpath wpath cpath tty sigaction", nullptr));
+    TRY(Core::System::pledge("stdio rpath wpath cpath tty sigaction", nullptr));
 #endif
 
     bool gc_on_every_allocation = false;