We were hitting a problem when reading the LANGUAGE/OPTIONS pragmas
from GHC.TypeLits, where the buffer ended "{-". The rules for the
start-comment lexeme check that "{-" is not followed by "#", but the
test returned False when there was no next character. Therefore we
were lexing this as as an open-curly lexeme (only consuming the "{",
and not reaching the end of the buffer),
which meant the options parser think that it had reached the end of
the options.

Now we correctly lex as "{-".