Update LuaJIT to 2.1.0-beta3

Highlights from Mike Pall [1]:

The major addition over beta2 is the LJ_GC64 mode JIT compiler
backend contributed by Peter Cawley. Previously, only the x64 and
ARM64 interpreters could be built in this mode. This mode removes
the 32 bit limitation for garbage collected memory on 64 bit systems.

LuaJIT for x64 can optionally be built for LJ_GC64 mode by
enabling the -DLUAJIT_ENABLE_GC64 line in src/Makefile or via
'msvcbuild.bat gc64'.

Cisco Systems, Inc. and Linaro have sponsored the development of
the JIT compiler backend for ARM64. Contributors are Djordje
Kovacevic and Stefan Pejic from RT-RK, Charles Baylis from Linaro
and Zheng Xu from ARM. ARM64 big endian mode is now supported, too.

Cisco Systems, Inc. has sponsored the development of the MIPS64
interpreter and JIT compiler backend. Contributors are Djordje
Kovacevic and Stefan Pejic from RT-RK.

Peter Cawley has contributed the changes for full exception
interoperability on Windows/x86 (32 bit).

François Perrad has contributed various extensions from Lua 5.2 and
Lua 5.3. Note: some left-over compatibility defines for Lua 5.0
have been removed from the header files.

[1]: https://www.freelists.org/post/luajit/LuaJIT210beta3

In context of #2396

luajit @ e6e25b42

-Subproject commit af88dded7bd2c8e5bb8b6bc86279bd2b81bb2f5f
+Subproject commit e6e25b42ecee28b9b801872d313fd36815386536