[flang][openacc] Update serial construct clauses for OpenACC 3.1

[clementval]

Summary

Update the allowed clauses for the SERIAL construct for the new OpenACC 3.1
specification.

[clementval]

Push correct patch version

[sameeranjoshi]

Thanks for the upgrade.
A comment below.

flang/test/Semantics/acc-clause-validity.f90

944

Adding clause except async and wait after device_type, will that be allowed ?

I see 3.0 had a restriction section(919) whereas 3.1 has no such restrictions, so does the relaxation from specification reflect in compiler as well?

there was one more
`At most one default clause may appear, and it must have a value of either none or
present.`
Other that none or present will they be allowed now?

[clementval]

flang/test/Semantics/acc-clause-validity.f90

944

Adding clause except async and wait after device_type, will that be allowed ?

No this is not allowed.

3.1 has the same restrictions as before for that but phrased differently
"(950) where clause is as for the parallel construct except that the num_gangs, num_workers, and"
"(951) vector_length clauses are not permitted."

So the default clause has the same restriction as parallel here as well

[clementval]

Rebase

[clementval]

Rebase 2