doxygen: enable cross referencing everywhere

doxygen \ref cross-references to groups or files from other libraries only work
when the .map file was present when the HTML was generated, and when that .map
file was listed in TAGFILES in the Doxyfile.

- Makefile.am: introduce a two-pass build for doxygen API docs.
  - First build pass makes sure the .tag files are present.
  - Second build pass picks up all the references, hence generates hyperlinks
    properly.
- Add all libraries to TAGFILES of all other libraries, so we can from now on
  freely criss-cross reference from everywhere to everywhere.
- Add all libraries' tag files as dependencies for all others.

Example: in upcoming tdef.h, I would like to cross reference to tdef_vty.h, and
vice versa, even though they are in libosmocore and libosmovty, respectively.
This is now possible.

We may still need to fix some problems with naming collisions, see for example
stats.h, which exists twice with identical doxygen handle (different source
dirs seems to not suffice for doxygen).

Change-Id: Ib03d0b70d536c8f1386def666c89106a840f7363

0 files changed, 0 insertions, 0 deletions