In OpenMP Version 5.1, the tile and unroll directives were added. When
using these directives, it is possible to nest them within other OpenMP
Loop Constructs. This patch enables the semantics to allow for this
behaviour on these specific directives. Any nested loops will be stored
within the initial Loop Construct until reaching the DoConstruct itself.
Relevant tests have been added, and previous behaviour has been retained
with no changes.
See also, #110008
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