Dead link in "data-files:" documentation.

[danidiaz]

The Accessing data files from package code section of the user guide has a dead link to a non-existent section about "prefix independence":

(see prefix independence)

Googling for it, it seems that section formerly belonged to the GHC User Guide—but it isn't present in the current GHC User Guide.

[andreasabel]

No, the section "prefix independence" is still present in the Cabal docs: https://github.com/haskell/cabal/blob/7d4ce4787cb3d4fe30d08953ad64d19456a77690/doc/setup-commands.rst#prefix-independence

Only the link broke, maybe by 3752c3e which moved the text from installing-packages.rst to setup-commands.rst
bb16112 fixed some links, but must have missed this one.

[andreasabel]

Fix in PR #7586.

[andreasabel]

I took away the "wierd bug award", as broken references are easy to creep in.
Broken refs can maybe be avoided by passing -n ("nitpick") to sphinx-build, see https://www.sphinx-doc.org/en/master/man/sphinx-build.html#cmdoption-sphinx-build-n. E.g., when I run with -n, this sleeping bug surfaces:

doc/cabal-project.rst:644: WARNING: 'envvar' reference target not found: PATH

I'll prepare a new PR that fixes this.

P.S.: For the Agda user-manual, we treat warnings as errors (-W --keep-going) and rebuild from scratch (-E, annoys me): https://github.com/agda/agda/blob/3a4df95062c9484953b0505e73f74453c09fa714/doc/user-manual/Makefile#L5