[configure.ac] Added --enable-reproducible and --with-source-date-epoch=TIME

Example of usage:
./autogen.sh
./configure ... \
--enable-reproducible \
--with-source-date-epoch=$(git log -1 --pretty=%ct)

make
make -C doc html

Makefile.config.in

@@ -50,7 +50,7 @@ INSTALL_SCRIPT = @INSTALL_SCRIPT@
 
 host = @host@
 
-ASCIIDOC = @PYTHON3@ $(top_srcdir)/doc/tools/asciidoc/asciidoc.py
+ASCIIDOC = LANG=C LANGUAGE=en CONFIG_REPRODUCIBLE=@CONFIG_REPRODUCIBLE@ SOURCE_DATE_EPOCH=@SOURCE_DATE_EPOCH@ @PYTHON3@ $(top_srcdir)/doc/tools/asciidoc/asciidoc.py
 ASCIIDOC_FLAGS = --unsafe
 AWK = @AWK@
 CATALOGS = @CATALOGS@

configure.ac

@@ -1600,12 +1600,22 @@ EL_ARG_ENABLE(CONFIG_UTF8, utf-8, [UTF-8],
 EL_ARG_DEPEND(CONFIG_COMBINE, combining, [CONFIG_UTF8:yes HAVE_WCWIDTH:yes], [Combining characters],
 	      [  --enable-combining      support Unicode combining characters (experimental)])
 
+EL_ARG_ENABLE(CONFIG_REPRODUCIBLE, reproducible, [Reproducible builds],
+	      [  --enable-reproducible   enable reproducible build])
+
 AC_ARG_ENABLE(weehoofooboomookerchoo,
               [
     Also check out the features.conf file for more information about features!
 	      ],
 	      [AC_MSG_ERROR(Are you strange, or what?)])
 
+SOURCE_DATE_EPOCH=
+AC_ARG_WITH(source-date-epoch,    [  --with-source-date-epoch=[TIME]
+                          set source date epoch for reproducible builds],
+            [SOURCE_DATE_EPOCH="$withval"])
+
+AC_SUBST(SOURCE_DATE_EPOCH)
+
 
 # ===================================================================
 # Decide whether to use TRE

doc/tools/asciidoc/asciidoc.py

@@ -1061,7 +1061,8 @@ class Document:
         self.safe = True        # Default safe mode.
     def init_attrs(self):
         # Set implicit attributes.
-        if os.environ.get('CONFIG_REPRODUCIBLE', ''):
+        repro = os.environ.get('CONFIG_REPRODUCIBLE', '')
+        if repro and repro != 'no':
             d = time.gmtime(int(os.environ.get('SOURCE_DATE_EPOCH', time.time())))
             self.attributes['localdate'] = time.strftime('%d-%b-%Y',d)
             s = time.strftime('%H:%M:%S %z',d)