[mm-common] doc-reference.am: Don't assume all existing html files shall be rebuilt

[Kjell Ahlstedt <kjellahl src gnome org>]

commit b7dcdf272c1e9fbac97472ff565852f9bc55ddc4
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Thu Aug 27 13:16:42 2015 +0200

    doc-reference.am: Don't assume all existing html files shall be rebuilt
    
    * build/doc-reference.am: Don't use the set of previously generated files as
    prerequisites when building reference documentation. Bug #686364.

 build/doc-reference.am |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)
---
diff --git a/build/doc-reference.am b/build/doc-reference.am
index d267d6d..94df2d5 100644
--- a/build/doc-reference.am
+++ b/build/doc-reference.am
@@ -76,10 +76,12 @@ doctools_dist_files =
 endif
 
 if ENABLE_DOCUMENTATION
+doc_build_files  = $(doxytagfile) $(devhelpfile)
 doc_inst_targets = install-htmlref install-devhelp
 doc_inst_files   = $(doxytagfile)
 doc_dist_files   = $(devhelpfile) $(call vpath_listall,$(htmlref_patterns))
 else
+doc_build_files  =
 doc_inst_targets =
 doc_inst_files   =
 doc_dist_files   =
@@ -140,8 +142,11 @@ endif
 # Export this variable for use in the Doxygen configuration file.
 export MMDOCTOOLDIR
 
-# Explicitly depend on the files to be distributed or installed.
-all-local: $(doc_inst_files) $(doc_dist_files)
+# Depend on files that we know shall be built.
+# $(call vpath_listall,$(htmlref_patterns)) is not used as a prerequisite.
+# It would expand to files that exist when the make command is issued,
+# which is not necessarily the set of files that shall be built.
+all-local: $(doc_build_files)
 
 # Hook up custom rules for translating references to external documentation
 # to the actual location at install time.