Move ZLIB from 'platforms' to 'features'

Having it as a 'platform' was conceptually wrong from from the
beginning, and makes decoding more complicated than necessary.
Reviewed-by: NTim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7191)

util/libcrypto.num

@@ -2529,7 +2529,7 @@ ASN1_STRING_type_new                    2494	1_1_0	EXIST::FUNCTION:
 TS_STATUS_INFO_free                     2495	1_1_0	EXIST::FUNCTION:TS
 BN_mod_mul                              2496	1_1_0	EXIST::FUNCTION:
 CMS_add0_recipient_key                  2497	1_1_0	EXIST::FUNCTION:CMS
-BIO_f_zlib                              2498	1_1_0	EXIST:ZLIB:FUNCTION:COMP
+BIO_f_zlib                              2498	1_1_0	EXIST::FUNCTION:COMP,ZLIB
 AES_cfb128_encrypt                      2499	1_1_0	EXIST::FUNCTION:
 ENGINE_set_EC                           2500	1_1_0	EXIST::FUNCTION:ENGINE
 d2i_ECPKParameters                      2501	1_1_0	EXIST::FUNCTION:EC

util/mkdef.pl

@@ -176,15 +176,12 @@ sub platform_filter {
 
 sub feature_filter {
     my $item = shift;
-    my %platforms = ( $item->platforms() );
     my @features = ( $item->features() );
 
     # True if no features are defined
-    return 1 if scalar @features == 0 && scalar keys %platforms == 0;
+    return 1 if scalar @features == 0;
 
-    my $verdict =
-        !( ( grep { $disabled_uc{$_} } @features )
-           || ( grep { $_ eq 'ZLIB' && $disabled_uc{$_} } keys %platforms ) );
+    my $verdict = ! grep { $disabled_uc{$_} } @features;
 
     if ($apiv) {
         foreach (@features) {

util/mknum.pl

@@ -79,7 +79,7 @@ my $aix=0;
 my $safe_stack_def = 0;
 
 my @known_platforms = ( "__FreeBSD__", "PERL5",
-			"EXPORT_VAR_AS_FUNCTION", "ZLIB", "_WIN32"
+			"EXPORT_VAR_AS_FUNCTION", "_WIN32"
 			);
 my @known_ossl_platforms = ( "UNIX", "VMS", "WIN32", "WINNT", "OS2" );
 my @known_algorithms = ( # These are algorithms we know are guarded in relevant
@@ -267,6 +267,7 @@ sub do_defs
 			_WINDLL		=> 0,
 			CONST_STRICT	=> 0,
 			TRUE		=> 1,
+			ZLIB		=> 0,
 		);
 		my $symhacking = $file eq $symhacksfile;
 		my @current_platforms = ();
@@ -524,6 +525,8 @@ sub do_defs
 				push @current_algorithms,
 				    grep { /^DEPRECATEDIN_/ && $tag{$_} == 1 }
 				    @known_algorithms;
+				push @current_algorithms, "ZLIB"
+				    if $tag{ZLIB} == 1;
 				$def .=
 				    "#INFO:"
 					.join(',',@current_platforms).":"
@@ -994,12 +997,11 @@ sub is_valid
 			if ($keyword eq "EXPORT_VAR_AS_FUNCTION" && $W32) {
 				return 1;
 			}
-			if ($keyword eq "ZLIB" && $zlib) { return 1; }
 			return 0;
 		} else {
 			# algorithms
 			if ($disabled_algorithms{$keyword}) { return 0;}
-
+			if ($keyword eq "ZLIB" && $zlib) { return 1; }
 			# Nothing recognise as true
 			return 1;
 		}