I chose to make two of them because I wanted something close to an
"end-to-end" test (*), but at the same time I wanted a test that
would run on Windows (**).
(*) The run-make test serves as the end-to-end: It constructs an input
that is trying to subvert the hack and we are going to check that it
fails in the attempt).
(**) The compile-fail-fulldeps test serves as a more narrow test that
will be tested on all platforms. It also attempts to subvert the
hack, testing that when you use `new_parser_from_tts`, the resulting
parser does not support reading embedded Idents.
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