fix the following 'make headers_check' warnings:

  usr/include/linux/elf.h:379: extern's make no sense in userspace
  usr/include/linux/elf.h:387: extern's make no sense in userspace
  usr/include/linux/elf.h:401: extern's make no sense in userspace
  usr/include/linux/elf.h:402: extern's make no sense in userspace
Signed-off-by: NJaswinder Singh Rajput <jaswinderrajput@gmail.com>