sanity: check for GNU tar specifically

We need the system tar to be GNU tar, as we reply on --xattrs.  Some
distributions may be using libarchive's tar binary, which is definitely
not as featureful, so check for this and abort early with a clear
message instead of later with mysterious errors.

(From OE-Core rev: fd92cdc6d2b9b3b808503b3274860a7c301587cb)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit 7dd2b1cd1bb10e67485dab8600c0787df6c2eee7)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-global/sanity.bbclass

@@ -504,6 +504,14 @@ def check_tar_version(sanity_data):
     version = result.split()[3]
     if bb.utils.vercmp_string_op(version, "1.28", "<"):
         return "Your version of tar is older than 1.28 and does not have the support needed to enable reproducible builds. Please install a newer version of tar (you could use the project's buildtools-tarball from our last release or use scripts/install-buildtools).\n"
+
+    try:
+        result = subprocess.check_output(["tar", "--help"], stderr=subprocess.STDOUT).decode('utf-8')
+        if "--xattrs" not in result:
+            return "Your tar doesn't support --xattrs, please use GNU tar.\n"
+    except subprocess.CalledProcessError as e:
+        return "Unable to execute tar --help, exit code %d\n%s\n" % (e.returncode, e.output)
+
     return None
 
 # We use git parameters and functionality only found in 1.7.8 or later