Make shift argument to eoshift0 and eoshift2 be of type index_type

Make shift argument to eoshift0 and eoshift2 be of type index_type

Test case that requires 4 GB RAM that exercises eoshift0:

program main
  implicit none
  integer(1) :: line(2_8**31+10)
  line = 42
  line = eoshift(line, 2_8**31+7)
  print *, line(1:4)
  print *, line((ubound(line, 1, kind=8)-4):ubound(line, 1, kind=8))
end program main

Before patch:
❯ ./a.out
    0    0    0    0
    42   42   42   42   42

With patch:
❯ ./a.out
   42   42   42    0
   0    0    0    0    0

Regtested on x86_64-pc-linux-gnu.

libgfortran/ChangeLog:

2017-11-22  Janne Blomqvist  <jb@gcc.gnu.org>

        * intrinsics/eoshift0.c (eoshift0): Make shift an index_type.
        * intrinsics/eoshift2.c (eoshift2): Make shift an index_type.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@255077 138bc75d-0d04-0410-961f-82ee72b054a4