contrib: macdeploy: monkey-patch gen-sdk to be deterministic

on different Python versions (there was a change in TAR handling
between Python 3.8 and Python 3.9)

contrib/macdeploy/gen-sdk

@@ -8,6 +8,21 @@ import gzip
 import os
 import contextlib
 
+# monkey-patch Python 3.8 and older to fix wrong TAR header handling
+# see https://github.com/bitcoin/bitcoin/pull/24534
+# and https://github.com/python/cpython/pull/18080 for more info
+if sys.version_info < (3, 9):
+    _old_create_header = tarfile.TarInfo._create_header
+    def _create_header(info, format, encoding, errors):
+        buf = _old_create_header(info, format, encoding, errors)
+        # replace devmajor/devminor with binary zeroes
+        buf = buf[:329] + bytes(16) + buf[345:]
+        # recompute checksum
+        chksum = tarfile.calc_chksums(buf)[0]
+        buf = buf[:-364] + bytes("%06o\0" % chksum, "ascii") + buf[-357:]
+        return buf
+    tarfile.TarInfo._create_header = staticmethod(_create_header)
+
 @contextlib.contextmanager
 def cd(path):
     """Context manager that restores PWD even if an exception was raised."""