sort directory listings

because ordering matters in some places
when we want to generate reproducible results

to fix https://bugzilla.gnome.org/show_bug.cgi?id=784177

See also https://reproducible-builds.org/docs/stable-inputs/ on that topic

Index: gtk-doc-1.25/gtkdoc-scan.in
===================================================================
--- gtk-doc-1.25.orig/gtkdoc-scan.in
+++ gtk-doc-1.25/gtkdoc-scan.in
@@ -223,7 +223,7 @@ sub ScanHeaders {
     opendir (SRCDIR, $source_dir)
         || die "Can't open source directory $source_dir: $!";
     my $file;
-    foreach $file (readdir (SRCDIR)) {
+    foreach $file (sort (readdir (SRCDIR))) {
         if ($file eq '.' || $file eq '..' || $file =~ /^\./) {
             next;
         } elsif (-d "$source_dir/$file") {
Index: gtk-doc-1.25/gtkdoc-fixxref.in
===================================================================
--- gtk-doc-1.25.orig/gtkdoc-fixxref.in
+++ gtk-doc-1.25/gtkdoc-fixxref.in
@@ -204,7 +204,7 @@ sub ScanIndices {
 
     opendir (HTMLDIR, $scan_dir) || return;
     my $file;
-    foreach $file (readdir (HTMLDIR)) {
+    foreach $file (sort (readdir (HTMLDIR))) {
         if ($file eq '.' || $file eq '..') {
             next;
         } elsif (-d "$scan_dir/$file") {
@@ -323,7 +323,7 @@ sub FixCrossReferences {
     opendir (HTMLDIR, $scan_dir)
         || die "Can't open HTML directory $scan_dir: $!";
     my $file;
-    foreach $file (readdir (HTMLDIR)) {
+    foreach $file (sort (readdir (HTMLDIR))) {
         if ($file eq '.' || $file eq '..') {
             next;
         } elsif ($file =~ m/.html?$/) {
Index: gtk-doc-1.25/gtkdoc-mkdb.in
===================================================================
--- gtk-doc-1.25.orig/gtkdoc-mkdb.in
+++ gtk-doc-1.25/gtkdoc-mkdb.in
@@ -3900,7 +3900,7 @@ sub ReadSourceDocumentation {
     opendir (SRCDIR, $source_dir)
         || die "Can't open source directory $source_dir: $!";
 
-    foreach $file (readdir (SRCDIR)) {
+    foreach $file (sort (readdir (SRCDIR))) {
       if ($file =~ /^\./) {
         next;
       } elsif (-d "$source_dir/$file") {
Index: gtk-doc-1.25/gtkdoc-rebase.in
===================================================================
--- gtk-doc-1.25.orig/gtkdoc-rebase.in
+++ gtk-doc-1.25/gtkdoc-rebase.in
@@ -157,7 +157,7 @@ sub ScanDirectory {
     my $file;
     my $onlinedir;
     my $have_index = 0;
-    foreach $file (readdir(HTMLDIR)) {
+    foreach $file (sort (readdir(HTMLDIR))) {
         if ($file eq '.' or $file eq '..') {
             next;
         }
@@ -291,7 +291,7 @@ sub RebaseReferences {
     my ($dir) = @_;
 
     opendir(HTMLDIR, $dir) || die "Can't open HTML directory $dir: $!";
-    foreach my $file (readdir(HTMLDIR)) {
+    foreach my $file (sort (readdir(HTMLDIR))) {
         if ($file =~ m/\.html?$/) {
             &RebaseFile("$dir$file");
         }