This patch updates the fortran FE to generate errors, rather than
warnings, for non-positive integer tile clause arguments. I noticed this
problem when I ported over the C/C++ compile time test cases to fortran.
In addition to the two new test files, a couple of other existing tests
needed to be updated to accommodate this new behavior. I've applied it
to gomp-4_0-branch.

Nathan, I haven't looked too deeply into your tile changes yet. Do you
know of the fortran FE is doing anything wrong? I haven't checked if
it's lowering the tile clause in the proper format yet.

Cesar