Fix #2531 — pass post and lang to compilers

[Kwpolska]

This is #2531. There isn’t anything else we could post to this function, so hopefully we won’t have to do real_compile next time.

cc @felixfontein, reviews welcome.

[felixfontein]

LGTM. No idea about the failing tests, though...

[Kwpolska]

This is so stupid. Apparently, is_one_file can make things break if set incorrectly (perhaps due to metadata splitting). I’ll fix it and merge.

[felixfontein]

Why not fix the test instead of (again) having the compilers compile signature disagree with the signature in PageCompiler?

[Kwpolska]

Or we can make the PageCompiler signature match.

And the problem is not really in the test. is_two_file set to False means some extra manipulation which should not be the default.