Resolving cross-references among components

[David Nečas <yeti physics muni cz>]

Hello, what is the recommended method/best practice for getting right
bidirectional cross-references in documentation?

Imagine a project that builds two libraries, libA and libB, with
separate documentation.  If documentation for libA is built while
index.sgml in libB documentation does not exist yet, cross-links from A
to B will not resolve.  And vice versa.  Even if B strictly depends on A
one may want to reference B from the documentation of A to point out
implementations of abstractions, more high-level facilities or other
code in B that builds on A's features.

Since index.sgml is distributed anyone who rebuilds the documentation
from a tarball will get cross-references both ways right.  But what
about fresh checkouts?  I can only think of two ways to get correct
cross-references, one uglier than the other:
- build documentation twice
- keep index.sgml in the version control system

Yeti