[llvm] [LoongArch] Add STACKMAP and PATCHPOINT lowering (PR #223921)

[via llvm-commits]

vincent-163 wrote:

> * Could you  add some tests in `llvm/unittests/Target/LoongArch/InstSizes.cpp`?

Doing

>     * Keep PR description the same as the commit. No need to mention the testing stuff.

Done

> 
>     * May I know where these two experimental intrinsics are used?

Currently I'm developing a binary translation project and these intrinsics are used for accurate exceptions. A stackmap is inserted before every potentially faulting instruction (such as memory access) so when it faults all the registers are available and we can resume guest execution.

https://github.com/llvm/llvm-project/pull/223921