Step 0: mk/ Update Minix platform definition

We are transitionning from a full platform to a NetBSD variant,
per the project policy of having a NetBSD userland. There is then
little meaning in adapting all the NetBSD tests to also be true for
Minix.

This means the following is set as:
 * OPSYS = NetBSD
 * OS_VARIANT = Minix

This also has the consequence of obsoleting a few files in
pkgtools/bootstrap-mk-files.

mk/gnu-config/config.guess

@@ -895,8 +895,8 @@ EOF
 	# other systems with GNU libc and userland
 	echo ${UNAME_MACHINE}-unknown-`echo ${UNAME_SYSTEM} | sed 's,^[^/]*/,,' | tr '[A-Z]' '[a-z]'``echo ${UNAME_RELEASE}|sed -e 's/[-(].*//'`-${LIBC}
 	exit ;;
-    i*86:Minix:*:*)
-	echo ${UNAME_MACHINE}-pc-minix
+    *:Minix:*:*)
+	echo ${UNAME_MACHINE}-elf32-minix
 	exit ;;
     aarch64:Linux:*:*)
 	echo ${UNAME_MACHINE}-unknown-linux-${LIBC}