This seems to be first stable linux version, released with sync-check.sh tool.
Problem appears during

make modules_prepare

, in postinst.
As seems for me, it tries to run non-executable script.

log below is from second run, after most part is done:

# LANG=C make modules_prepare
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  DESCEND  objtool
make[2]: execvp: ./sync-check.sh: Permission denied