OpenACC in Flang

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Intentional deviation from the specification

See OpenACC-extensions.md for the full list of extensions supported by Flang. Flang also adds the following restrictions:

• The OpenACC specification does not prohibit the same variable from appearing in multiple data clauses, but this is disallowed for variables appearing in reduction clauses.
• The OpenACC specification does not prohibit the same variable from appearing multiple times in a use_device clause on a host_data construct, but this is disallowed.

Remarks about incompatibilities with other implementations

• Array element references in the data clauses are equivalent to array sections consisting of this single element, i.e. copyin(a(n)) is equivalent to copyin(a(n:n)). Some other implementations have treated it as copyin(a(:n)), which does not correspond to OpenACC spec – Flang does not support this interpretation of an array element reference.