Update luajit to git master version

[YunQiang Su <wzssyqa@gmail.com>]

The current luajit version is very old, and it makes some trouble to
build some packages for MIPS.

So I uploaded the git master version of luajit to experimental.
The changelog is:
 luajit (2.1.0~beta3+git20210112+dfsg-1~exp) experimental; urgency=medium

   * Team upload.
   * Update to current git master version.
   * Bump compact to 12.
   * Bump standard version to 4.5.1.0.
   * Vcs-*: switch to salsa.
   * MIPS: enable all architectures: r6 is now supported
   * PPC: refresh ppc64 support patch.
   * Remove patches has been included in upstream:
     - 0005-Make-ccall_copy_struct-static-to-unpollute-global-li.patch
     - 362.patch
     - a057a07ab702e225e21848d4f918886c5b0ac06b.patch
     - e9af1abec542e6f9851ff2368e7f196b6382a44c.patch
   * Remove 0006-Fix-register-allocation-bug-in-arm64.patch: seems not
needed now.

@powerpc folks:
I am not so confident that the refresh of the ppc64 support patch is
correct. Can you help me to have a review and test of it.
@ARM64 folks:
Is just removing 0006-Fix-register-allocation-bug-in-arm64.patch correct?

-- 
YunQiang Su