This clause is pretty small/doesn't do much semantic-analysis-wise, , other than
have two spellings and disallow certain clauses after it. However, as
most of those aren't implemented yet, the diagnostic is left as a TODO.
These three are identical to the version on compute constructs, so this
patch implements the tests for it, and ensures that we properly validate
it against all the other clauses we're supposed to. The test is mostly
a mock-up at the moment, since most other clauses aren't implemented
yet for 'loop'.
Combined constructs (OpenACC 3.3 section 2.11) are a short-cut for
writing a `loop` construct immediately inside of a `compute` construct.
However, this interaction requires we do additional work to ensure that
we get the semantics between the two correct, as well as diagnostics.
This patch adds the semantic analysis for the constructs (but no
clauses), as well as the AST nodes.
