Squashed 'luajit/' changes from 7e538b5..f371ed6

f371ed6 Respect jit.off(func) when returning to a function, too.
9d90988 Follow-up fix for GC step threshold fix.
751eace Improve msvcbuild.bat static linking.
db64b2b FFI: Clarify ffi.cdef behavior.
5a25a73 Fix type punning alias analysis for constified pointers.
8941b19 Fix for last commit
7b4d530 Fix GC steps threshold handling when called by JIT-compiled code.
8944e27 Fix handling of redundant PHIs.

git-subtree-dir: luajit
git-subtree-split: f371ed6bd8741834b4b0278cf2c9e95e32f2cb26
Merge commit 'e1fd7ebf04a4899336c3365ba25ab2c01766068c'