Enable IBT(Indirect Branch Tracking) in JIT with CET(Control-flow Enforcement Technology)

Do not commit the llvm/test/ExecutionEngine/MCJIT/cet-code-model-lager.ll because it will
cause build bot fail(not suitable for window 32 target).

Summary:
This patch comes from H.J.'s https://github.com/hjl-tools/llvm-project/commit/2bd54ce7fa9e94fcd1118b948e14d1b6fc54dfd2

This patch fix the failed llvm unit tests which running on CET machine. (e.g. ExecutionEngine/MCJIT/MCJITTests)

The reason we enable IBT at "JIT compiled with CET" is mainly that: the JIT don't know the its caller program is CET enable or not.
If JIT's caller program is non-CET, it is no problem JIT generate CET code or not.
But if JIT's caller program is CET enabled, JIT must generate CET code or it will cause Control protection exceptions.

I have test the patch at llvm-unit-test and llvm-test-suite at CET machine. It passed.
and H.J. also test it at building and running VNCserver(Virtual Network Console), it works too.
(if not apply this patch, VNCserver will crash at CET machine.)

Reviewers: hjl.tools, craig.topper, LuoYuanke, annita.zhang, pengfei

Reviewed By: LuoYuanke

Subscribers: tstellar, efriedma, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76900

(cherry picked from commit 01a32f2bd3fad4331cebe9f4faa270d7c082d281)