Merge branch 'doc/4.3-reproducible' into docs-next

Ben Hutchings writes:

As part of the reproducible builds project, Jérémy Bobbio identified
several time-dependent and non-deterministic functions in the document
build process (htmldocs, mandocs targets). This patch series should fix
all of those.

I ended up reverting one patch that introduced problems.

Documentation/DocBook/Makefile

···
 
 MAN := $(patsubst %.xml, %.9, $(BOOKS))
 mandocs: $(MAN)
-	find $(obj)/man -name '*.9' | xargs gzip -f
+	find $(obj)/man -name '*.9' | xargs gzip -nf
 
 installmandocs: mandocs
 	mkdir -p /usr/local/man/man9/

Documentation/DocBook/stylesheet.xsl

···
 <param name="funcsynopsis.tabular.threshold">80</param>
 <param name="callout.graphics">0</param>
 <!-- <param name="paper.type">A4</param> -->
+<param name="generate.consistent.ids">1</param>
 <param name="generate.section.toc.level">2</param>
 <param name="use.id.as.filename">1</param>
 </stylesheet>

scripts/kernel-doc

···
 my $blankline = $blankline_man;
 my $modulename = "Kernel API";
 my $function_only = 0;
+my $show_not_found = 0;
+
+my @build_time;
+if (defined($ENV{'KBUILD_BUILD_TIMESTAMP'}) &&
+    (my $seconds = `date -d"${ENV{'KBUILD_BUILD_TIMESTAMP'}}" +%s`) ne '') {
+    @build_time = gmtime($seconds);
+} else {
+    @build_time = localtime;
+}
+
 my $man_date = ('January', 'February', 'March', 'April', 'May', 'June',
 		'July', 'August', 'September', 'October',
-		'November', 'December')[(localtime)[4]] .
-  " " . ((localtime)[5]+1900);
-my $show_not_found = 0;
+		'November', 'December')[$build_time[4]] .
+  " " . ($build_time[5]+1900);
 
 # Essentially these are globals.
 # They probably want to be tidied up, made more localised or something.
···
 
 # generate a sequence of code that will splice in highlighting information
 # using the s// operator.
-foreach my $pattern (keys %highlights) {
+foreach my $pattern (sort keys %highlights) {
 #   print STDERR "scanning pattern:$pattern, highlight:($highlights{$pattern})\n";
     $dohighlight .=  "\$contents =~ s:$pattern:$highlights{$pattern}:gs;\n";
 }