Revert "docs: Drop unused rule for internals/%.html.tmp target"

This reverts commit e5470dd0e0.

This has been ACK'd by the original author in the original mail thread:
https://www.redhat.com/archives/libvir-list/2015-September/msg00310.html

The reason to revert this is due to the patch breaking the generation of
internal subsites.  The original issue still needs to be dealt with,
though.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

configure.ac

@@ -2777,7 +2777,6 @@ AC_DEFINE_UNQUOTED([isbase64],[libvirt_gl_isbase64],[Hack to avoid symbol clash]
 AC_DEFINE_UNQUOTED([base64_encode],[libvirt_gl_base64_encode],[Hack to avoid symbol clash])
 AC_DEFINE_UNQUOTED([base64_encode_alloc],[libvirt_gl_base64_encode_alloc],[Hack to avoid symbol clash])
 
-AC_CONFIG_COMMANDS([mkdir], [$MKDIR_P docs/internals])
 AC_CONFIG_FILES([run],
                 [chmod +x,-w run])
 AC_CONFIG_FILES([\

docs/Makefile.am

@@ -218,6 +218,15 @@ $(srcdir)/hvsupport.html.in: $(srcdir)/hvsupport.pl $(api_DATA) \
 %.png: %.fig
 	convert -rotate 90 $< $@
 
+internals/%.html.tmp: internals/%.html.in subsite.xsl page.xsl sitemap.html.in
+	@if [ -x $(XSLTPROC) ] ; then \
+	  echo "Generating $@"; \
+	  $(MKDIR_P) internals; \
+	  name=`echo $@ | sed -e 's/.tmp//'`; \
+	  $(XSLTPROC) --stringparam pagename $$name --nonet \
+	    $(top_srcdir)/docs/subsite.xsl $< > $@ \
+	    || { rm $@ && exit 1; }; fi
+
 %.html.tmp: %.html.in site.xsl page.xsl sitemap.html.in $(acl_generated)
 	@if [ -x $(XSLTPROC) ] ; then \
 	  echo "Generating $@"; \