Hi!
Move is_vsyscall_vaddr() into asm/vsyscall.h to make it available for
copy_from_kernel_nofault_allowed() in arch/x86/mm/maccess.c.
This seems to be just part of a patch -- it does not move anything --
and we should not really need it for 4.19, as we don't have those
copy_from_kernel_nofault_allowed changes.