Re #3, @sunita.
I am trying to compile the linux kernel with simple hello world program
Many of the "hello world program`s" you can find are ancient.
I.e. for a very old kernel.
So unless your "hello world" was written yesterday, it may fail.
#include <linux/modulbuild.h> /
modulbuild.h is an unknown file.
No file by name modulbuild.h or modulebuild.h ever existed.