[glibmm] docs/reference/: Update for Doxygen >= 1.8.16

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 4976714d10dd6cd32b04f358a390fdc38f8bcd2f
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Mon Jun 29 15:03:31 2020 +0200

    docs/reference/: Update for Doxygen >= 1.8.16
    
    * docs/reference/meson.build: Doxygen 1.8.16 and later does not store
    tag file names in the html files. This requires changes in meson.build
    and in doc-install.pl (in mm-common). Otherwise references to other modules
    won't be updated in the html files when they are installed.
    * docs/reference/Doxyfile.in: Remove PERL_PATH and MSCGEN_PATH.
    Doxygen since version 1.8.0 does not use them.

 docs/reference/Doxyfile.in |  2 --
 docs/reference/meson.build | 15 ++++++++-------
 2 files changed, 8 insertions(+), 9 deletions(-)
---
diff --git a/docs/reference/Doxyfile.in b/docs/reference/Doxyfile.in
index 5b4820c9..4712093f 100644
--- a/docs/reference/Doxyfile.in
+++ b/docs/reference/Doxyfile.in
@@ -319,12 +319,10 @@ GENERATE_TAGFILE       = "reference/@GLIBMM_MODULE_NAME@.tag"
 ALLEXTERNALS           = NO
 EXTERNAL_GROUPS        = NO
 EXTERNAL_PAGES         = YES
-PERL_PATH              = @PERL@
 #---------------------------------------------------------------------------
 # Configuration options related to the dot tool
 #---------------------------------------------------------------------------
 CLASS_DIAGRAMS         = YES
-MSCGEN_PATH            =
 DIA_PATH               =
 HIDE_UNDOC_RELATIONS   = NO
 HAVE_DOT               = YES
diff --git a/docs/reference/meson.build b/docs/reference/meson.build
index 029a61cf..790d1434 100644
--- a/docs/reference/meson.build
+++ b/docs/reference/meson.build
@@ -1,10 +1,9 @@
 # docs/reference
 
 # Input: built_files_root, project_source_root, glibmm_pcname, giomm_pcname,
-#        perl, glibmm_hg_ccg_basenames, giomm_hg_ccg_basenames,
+#        glibmm_hg_ccg_basenames, giomm_hg_ccg_basenames, build_documentation,
 #        glibmm_extra_h_files, giomm_extra_h_files, glibmm_built_h_file_targets,
-#        giomm_built_h_file_targets, install_datadir,python3, doc_reference_py,
-#        build_documentation
+#        giomm_built_h_file_targets, install_datadir,python3, doc_reference_py
 # Output: install_docdir, install_devhelpdir
 
 tag_file_modules = [
@@ -25,10 +24,13 @@ foreach module : tag_file_modules
       htmlrefdir = htmlrefpub
     endif
     doxygen_tagfiles += ' "' + doxytagfile + '=' + htmlrefpub + '"'
-    if not htmlrefdir.endswith('/')
-      htmlrefdir += '/'
-    endif
+
+    # Doxygen <= 1.8.15
     docinstall_flags += ['-l', doxytagfile.split('/')[-1] + '@' + htmlrefdir]
+    if htmlrefpub != htmlrefdir
+      # Doxygen >= 1.8.16
+      docinstall_flags += ['-l', 's@' + htmlrefpub + '@' + htmlrefdir]
+    endif
   endif
 endforeach
 
@@ -45,7 +47,6 @@ doc_conf_data.set('abs_top_builddir', built_files_root)
 doc_conf_data.set('abs_top_srcdir', project_source_root)
 doc_conf_data.set('GLIBMM_MODULE_NAME', book_name)
 doc_conf_data.set('DOXYGEN_TAGFILES', doxygen_tagfiles)
-doc_conf_data.set('PERL', perl.found() ? perl.path() : '')
 
 configure_file(
   input: 'Doxyfile.in',