On OpenBSD fchown(2) may deny changing the group of a file even if

the new group is the same as the old one.  Test of devel/p5-Alien-Base
fails due to xz failure.  Not calling fchown(2) in cases where the
group would not change anyway, fixes both.  Patch discussed with
upstream and cerry-picked from there.
OK naddy@

archivers/xz/Makefile

@@ -1,8 +1,9 @@
-# $OpenBSD: Makefile,v 1.38 2020/03/26 20:44:51 naddy Exp $
+# $OpenBSD: Makefile,v 1.39 2021/11/02 15:47:53 bluhm Exp $
 
 COMMENT=	LZMA compression and decompression tools
 
 DISTNAME=	xz-5.2.5
+REVISION=	0
 SHARED_LIBS=	lzma                 2.1      # 7.5
 CATEGORIES=	archivers
 DPB_PROPERTIES=	parallel

archivers/xz/patches/patch-src_xz_file_io_c

@@ -0,0 +1,24 @@
+$OpenBSD: patch-src_xz_file_io_c,v 1.3 2021/11/02 15:47:53 bluhm Exp $
+
+fix a test failure in a Perl module
+https://github.com/PerlAlien/Alien-Build/issues/62
+https://git.tukaani.org/?p=xz.git;a=commitdiff;h=892b16cc282f5b4e1c49871b326f4db25c5b4d81
+
+Index: src/xz/file_io.c
+--- src/xz/file_io.c.orig
++++ src/xz/file_io.c
+@@ -368,7 +368,13 @@ io_copy_attrs(const file_pair *pair)
+ 
+ 	mode_t mode;
+ 
+-	if (fchown(pair->dest_fd, (uid_t)(-1), pair->src_st.st_gid)) {
++	// With BSD directory semantics the new dest file may have a group
++	// which does not belong to the user.  If the src file has the same
++	// group, nothing has to be done.  Nevertheless OpenBSD fchown(2)
++	// fails in this case which looks POSIX compliant.  Linux does not
++	// generate an error.  As there is nothing to do, skip the syscall.
++	if (pair->dest_st.st_gid != pair->src_st.st_gid &&
++	    fchown(pair->dest_fd, (uid_t)(-1), pair->src_st.st_gid)) {
+ 		message_warning(_("%s: Cannot set the file group: %s"),
+ 				pair->dest_name, strerror(errno));
+ 		// We can still safely copy some additional permissions: