These two constructs are very simple and similar, and only support 3
different clauses, two of which are already implemented. This patch
adds AST nodes for both constructs, and leaves the device_num clause
unimplemented, but enables the other two.
'wait' takes a few int-exprs (well, a series of async-arguments, but
those are effectively just an int-expr), plus a pair of tags. This
patch adds the support for this to the AST, and does the appropriate
semantic analysis for them.
