add and migrate constants from ctypes/__init__.pyi to _ctypes.pyi (#8643)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Akuli <akuviljanen17@gmail.com>

stdlib/_ctypes.pyi

@@ -2,6 +2,13 @@ import sys
 from ctypes import _CArgObject, _PointerLike
 from typing_extensions import TypeAlias
 
+FUNCFLAG_CDECL: int
+FUNCFLAG_PYTHONAPI: int
+FUNCFLAG_USE_ERRNO: int
+FUNCFLAG_USE_LASTERROR: int
+RTLD_GLOBAL: int
+RTLD_LOCAL: int
+
 if sys.version_info >= (3, 11):
     CTYPES_MAX_ARGCOUNT: int