Addressing reviewers (3): tests now in veclib-function-calls.ll

Rebased history to introduce tests in 'veclib-function-calls.ll' and
delete the (now unnecessary) test veclib-function-calls-linear-ptrs.ll.

The commit history were modified as follows:
- The initial commit (that showcases what was missing) was amended to
  add the tests in veclib-function-calls.ll.
- Then, subsequent commits were similarly amended to include the updates
  that allow vectorization.
- This current commit simply dropped the no longer needed tests
  (veclib-function-calls-linear-ptrs.ll)

Author: paschalis-mpeis