[libxslt] Add Makefile rule to regenerate xsltproc.html

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 5f575507549da889660617290606e5cc437fc8ab
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Wed Feb 16 16:22:01 2022 +0100

    Add Makefile rule to regenerate xsltproc.html
    
    This file has never been updated since it was added 15 years ago.

 doc/Makefile.am | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/doc/Makefile.am b/doc/Makefile.am
index b99bf382..5cc4f3b8 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -140,7 +140,7 @@ man_MANS = xsltproc.1
 
 if REBUILD_DOCS
 
-all-local:     web ../NEWS libxslt.xsa $(man_MANS)
+all-local:     web ../NEWS libxslt.xsa $(man_MANS) xsltproc.html
 
 api:   libxslt-api.xml libxslt-refs.xml $(APIPAGES) search.php \
         html/index.html $(WIN32_DIR)/libxslt.def.src
@@ -242,6 +242,9 @@ libxslt-api.xml libxslt-refs.xml EXSLT/libexslt-api.xml \
        ($(XSLTPROC) $(srcdir)/checkapisym.xsl $(srcdir)/libxslt-api.xml)
        ($(XSLTPROC) -o ../libxslt/libxslt.syms $(srcdir)/syms.xsl $(srcdir)/symbols.xml)
 
+xsltproc.html: xsltproc.xml
+       -@($(XSLTPROC) --nonet -o $@ http://docbook.sourceforge.net/release/xsl/current/html/docbook.xsl 
xsltproc.xml)
+
 xsltproc.1: $(srcdir)/xsltproc.xml
        -@(if [ -x $(XSLTPROC) ] ; then \
           echo "Rebuilding the man pages from the xml" ; \