Use rel2abs() on VMS, rather than realpath()

It seems realpath() is quite buggy on VMS, or will at least give quite
surprising results.  On the other hand, realpath() is the better on
Unix to clean out clutter like foo/../bar on Unix.

So we make out own function to get the absolute directory for a given
input, and use rel2abs() or realpath() depending on the platform
Configure runs on.

Issue reported by Steven M. Schweda <sms@antinode.info>
Reviewed-by: NAndy Polyakov <appro@openssl.org>

Configure

@@ -12,7 +12,6 @@ use strict;
 use File::Basename;
 use File::Spec::Functions qw/:DEFAULT abs2rel rel2abs/;
 use File::Path qw/mkpath/;
-use Cwd qw/:DEFAULT realpath/;
 
 # see INSTALL for instructions.
 
@@ -142,8 +141,8 @@ sub resolve_config;
 # Information collection #############################################
 
 # Unified build supports separate build dir
-my $srcdir = catdir(realpath(dirname($0))); # catdir ensures local syntax
-my $blddir = catdir(realpath("."));       # catdir ensures local syntax
+my $srcdir = catdir(absolutedir(dirname($0))); # catdir ensures local syntax
+my $blddir = catdir(absolutedir("."));         # catdir ensures local syntax
 my $dofile = abs2rel(catfile($srcdir, "util/dofile.pl"));
 
 $config{sourcedir} = abs2rel($srcdir);
@@ -1180,22 +1179,14 @@ if ($builder eq "unified") {
     use lib catdir(dirname(__FILE__),"util");
     use with_fallback qw(Text::Template);
 
-    # Helpers to produce clean paths with no /../ in the middle and so on.
-    sub int_absolutedir {
-        my $dir = shift;
-
-        # Required, because realpath only works properly with existing dirs
-        mkpath($dir);
-
-        my $res = realpath($dir);
-        return $res;
-    }
-
     sub cleandir {
         my $dir = shift;
         my $base = shift || ".";
 
-        my $res = abs2rel(int_absolutedir($dir), rel2abs($base));
+        # Make sure the directories we're building in exists
+        mkpath($dir);
+
+        my $res = abs2rel(absolutedir($dir), rel2abs($base));
         #print STDERR "DEBUG[cleandir]: $dir , $base => $res\n";
         return $res;
     }
@@ -1206,7 +1197,10 @@ if ($builder eq "unified") {
         my $d = dirname($file);
         my $f = basename($file);
 
-        my $res = abs2rel(catfile(int_absolutedir($d), $f), rel2abs($base));
+        # Make sure the directories we're building in exists
+        mkpath($d);
+
+        my $res = abs2rel(catfile(absolutedir($d), $f), rel2abs($base));
         #print STDERR "DEBUG[cleanfile]: $d , $f => $res\n";
         return $res;
     }
@@ -2209,6 +2203,29 @@ sub print_table_entry
 
 # Utility routines ###################################################
 
+# Makes a directory absolute and cleans out /../ in paths like foo/../bar
+# On some platforms, this uses rel2abs(), while on others, realpath() is used.
+# realpath() requires that at least all path components except the last is an
+# existing directory.  On VMS, the last component of the directory spec must
+# exist.
+sub absolutedir {
+    my $dir = shift;
+
+    # realpath() is quite buggy on VMS.  It uses LIB$FID_TO_NAME, which
+    # will return the volume name for the device, no matter what.  Also,
+    # it will return an incorrect directory spec if the argument is a
+    # directory that doesn't exist.
+    if ($^O eq "VMS") {
+        return rel2abs($dir);
+    }
+
+    # We use realpath() on Unix, since no other will properly clean out
+    # a directory spec.
+    use Cwd qw/realpath/;
+
+    return realpath($dir);
+}
+
 sub which
 	{
 	my($name)=@_;