Doxygen: enable tagfile generation and usage for cross-project references

We also don't remove the html/ component of the path to be consistent with
libosmocore and allow possible future installation of pdf/latex/...

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

Doxyfile.in

@@ -1490,7 +1490,7 @@ TAGFILES               =
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
 
-GENERATE_TAGFILE       =
+GENERATE_TAGFILE       = doc/libosmodsp.tag
 
 # If the ALLEXTERNALS tag is set to YES all external classes will be listed
 # in the class index. If set to NO only the inherited external classes

Makefile.am

@@ -27,12 +27,12 @@ $(top_builddir)/doc/html/index.html: $(SOURCES) Doxyfile
 	$(DOXYGEN) Doxyfile
 
 install-data-hook:
-	cd $(DESTDIR)$(htmldir) && tar xf html.tar --strip-components 1 && rm -f html.tar
+	cd $(DESTDIR)$(htmldir) && tar xf html.tar && rm -f html.tar
 
 uninstall-hook:
 	rm -rf $(DESTDIR)$(htmldir)
 
-DX_CLEAN = doc/html/search/* doc/{html,latex}/* doc/html.tar
+DX_CLEAN = doc/html/search/* doc/{html,latex}/* doc/html.tar doc/*.tag
 
 endif