[C++] Pin flatbuffers compiler version

[bkietz]

Describe the bug, including details regarding any error messages, version, and platform.

I ran cpp/build-support/update-flatbuffers.sh and the regenerated headers included new failing static assertions like:

/home/ben/arrow/cpp/src/generated/Message_generated.h:11:41: error: static assertion failed: Non-compatible flatbuffers version included
   11 | static_assert(FLATBUFFERS_VERSION_MAJOR == 23 &&

The probable fix is to pin the version of the flatbuffers compiler used in c++. As of google/flatbuffers#7203 the compiler inserts these static assertions which assert the version of the compiler- but our vendored flatbuffers are at 1.12.0. conda-forge has that version and after installing it I don't see failing static assertions any more.

Component(s)

C++

[pitrou]

If we do this, we should first bump our vendored version of flatbuffers headers to a recent well-known changeset.

[pitrou]

cc @felipecrv