Minor improvement in gitinfo.h production

* Makefile.am: Minor change.
* include/mailutils/Makefile.am (gitinfo.h): Build only if
$(srcdir) and $(builddir) are the same.
* mu-aux/gitinfo.pl: Rename to mu-aux/gitinfo
* configure.ac (GITINFO): Reflect this change
* mu-aux/Makefile.am: Likewise.

@@ -123,13 +123,12 @@ SUBDIRS = . \
 EXTRA_DIST = COPYING.LESSER paths
 DISTCLEANFILES = pathdefs.h
 
-# Trigger creation of the ChangeLog
-noinst_DATA = ChangeLog
-
 gen_start_date = "2008-12-08"
 prev_change_log = "doc/ChangeLog.CVS"
-amend_file=ChangeLog.amend
+amend_file = ChangeLog.amend
 
+# Trigger creation of the ChangeLog
+noinst_DATA = ChangeLog
 .PHONY: ChangeLog
 ChangeLog: 
 	$(AM_V_at)if test -d .git; then					\
@@ -138,6 +137,8 @@ ChangeLog:
 		    --append=$(prev_change_log)     		        \
                     --amend=$(amend_file)                               \
 	            --since=$(gen_start_date);    			\
+	elif test "$(builddir)" = "$(srcdir)" && test ! -e ChangeLog; then \
+	    echo "This file is a placeholder." > ChangeLog;             \
 	fi
 
 dist-hook: ChangeLog

@@ -1374,7 +1374,7 @@ AC_PATH_PROG([PERL], perl)
 if test -z "$PERL"; then
   PERL=false
 fi  
-AC_SUBST([GITINFO],'$(PERL) $(mu_aux_dir)/gitinfo.pl')
+AC_SUBST([GITINFO],'$(PERL) $(mu_aux_dir)/gitinfo')
 
 AC_CONFIG_COMMANDS([status],[
 cat <<EOF

@@ -27,12 +27,13 @@ types.h: $(top_srcdir)/include/mailutils/types.hin Makefile
                    $(top_srcdir)/include/mailutils/types.hin > types.h
 
 gitinfo.h: $(top_srcdir)/ChangeLog
-	$(AM_V_GEN)if ! $(GITINFO) -Hc -ogitinfo.h \
-           && test ! -f $(srcdir)/gitinfo.h; then \
-	  echo '/* no info */' > gitinfo.h;\
+	$(AM_V_GEN)if test "$(builddir)" = "$(srcdir)"; then	\
+	   test -d $(top_srcdir)/.git && $(GITINFO) -Hc -ogitinfo.h; \
+	   if test ! -f gitinfo.h; then \
+	     echo '/* no info */' > gitinfo.h;\
+	   fi; \
 	fi
 
-
 DISTCLEANFILES = types.h
 
 pkginclude_HEADERS = \

@@ -23,7 +23,7 @@ EXTRA_DIST = \
  texify.sed\
  sqlmod.sh\
  generr.awk\
- gitinfo.pl
+ gitinfo
 
 m4datadir = $(datadir)/aclocal
 dist_m4data_DATA = mailutils.m4

+eval '(exit $?0)' && eval 'exec perl -wS "$0" "$@"'
+  & eval 'exec perl -wS "$0" $argv:q'
+    if 0;
+
 # This file is part of GNU Mailutils.
 # Copyright (C) 2017 Free Software Foundation, Inc.
 #
@@ -443,6 +447,7 @@ EOT
     'all' => sub {
 	foreach my $name (sort keys %gitinfo) {
 	    my $val = $gitinfo{$name};
+	    next unless defined $val;
 	    $val =~ s/(["\\])/\\$1/g;
 	    print "$name=\"$val\"\n";
 	}