[Flang][OpenMP] Add restriction about subobjects to firstprivate and … (#89608)

…lastprivate

OpenMP 5.2 standard (Section 5.3) defines privatization for list items.
Section 3.2.1 in the standard defines list items to exclude variables
that are part of other variables.

This patch adds the restriction to firstprivate and lastprivates, it was
previously added for privates.

Fixes https://github.com/llvm/llvm-project/issues/67227

Note: The specific checks that are added here are explicitly called out
in OpenMP 4.0
(https://www.openmp.org/wp-content/uploads/OpenMP4.0.0.pdf) Sections
2.14.3.4 and 2.14.3.5 but in later standards have become implicit
through other definitions.