Patch implements restrictions from 2.17.7 of OpenMP 5.0 standard for atomic Construct. Tests for the same are added.
One of the restriction
`OpenMP constructs may not be encountered during execution of an atomic region.`
Is mentioned in 5.0 standard to be a semantic restriction, but given the stricter nature of parser in F18 it's caught at parsing itself.
This patch is a next patch in series from D88965.
Reviewed By: clementval
Differential Revision: https://reviews.llvm.org/D89583
sameeran joshi