rdoc: build reproducible documentation

- sort input filenames
- provide a fixed timestamp to the gzip compression

Signed-off-by: Antonio Terceiro <terceiro@debian.org>
Signed-off-by: Christian Hofstaedtler <zeha@debian.org>

Gbp-Pq: Name rdoc-build-reproducible-documentation.patch

Author: zeha

lib/rdoc/generator/json_index.rb

@@ -178,7 +178,7 @@ def generate_gzipped
     debug_msg "Writing gzipped search index to %s" % outfile
 
     Zlib::GzipWriter.open(outfile) do |gz|
-      gz.mtime = File.mtime(search_index_file)
+      gz.mtime = -1
       gz.orig_name = search_index_file.basename.to_s
       gz.write search_index
       gz.close
@@ -196,7 +196,7 @@ def generate_gzipped
         debug_msg "Writing gzipped file to %s" % outfile
 
         Zlib::GzipWriter.open(outfile) do |gz|
-          gz.mtime = File.mtime(dest)
+          gz.mtime = -1
           gz.orig_name = dest.basename.to_s
           gz.write data
           gz.close