[flang] Split doconcurrent04.f90 test into one with expression checks and one...

[flang] Split doconcurrent04.f90 test into one with expression checks and one for later semantics pass.

Original-commit: flang-compiler/f18@6b9c25177b606eca0cb9d8d47dd1d5ac1ee7635b
Reviewed-on: https://github.com/flang-compiler/f18/pull/406
Tree-same-pre-rewrite: false