We don't actually probe for javac in all circumstances, so if you have
javac installed, but don't have antlr4 installed, and you're on Mac OS
X, then you'll get a message that javac is missing, even though that's
wrong.
To fix this, let's just be a bit more generic in the message, so that
it's the same no matter what part of the lexer tests you're missing.
cc
https://www.reddit.com/r/rust/comments/3m199d/running_make_check_on_the_source_code_says_javac/
f78115434c