[clang] [llvm] [BPF] Add load-acquire and store-release instructions under -mcpu=v5 (PR #108636)

[via cfe-commits]

eddyz87 wrote:

@peilin-ye ,

> Got it, rebased and added a 4th commit (can't say I like the one-commit-per-PR policy either :-) to do this in v3. Please take another look.

lgtm, but please note CI failure:

```
_bk;t=1727211158841FAIL: LLVM :: CodeGen/BPF/acquire-release.ll (11379 of 55168)
_bk;t=1727211158841******************** TEST 'LLVM :: CodeGen/BPF/acquire-release.ll' FAILED ********************
_bk;t=1727211158841Exit Code: 2
_bk;t=1727211158841
_bk;t=1727211158841Command Output (stdout):
_bk;t=1727211158841--
_bk;t=1727211158841# RUN: at line 1
_bk;t=1727211158841c:\ws\src\build\bin\llc.exe < C:\ws\src\llvm\test\CodeGen\BPF\acquire-release.ll -march=bpfel -mcpu=v5 -verify-machineinstrs -show-mc-encoding | c:\ws\src\build\bin\filecheck.exe C:\ws\src\llvm\test\CodeGen\BPF\acquire-release.ll
_bk;t=1727211158841# executed command: 'c:\ws\src\build\bin\llc.exe' -march=bpfel -mcpu=v5 -verify-machineinstrs -show-mc-encoding
_bk;t=1727211158841# .---command stderr------------
_bk;t=1727211158841# | Assertion failed: From.getNode() != To.getNode() && "Potential legalization loop!", file C:\ws\src\llvm\lib\CodeGen\SelectionDAG\LegalizeTypes.cpp, line 646
_bk;t=1727211158841# | PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
_bk;t=1727211158841# | Stack dump:
_bk;t=1727211158841# | 0.	Program arguments: c:\\ws\\src\\build\\bin\\llc.exe -march=bpfel -mcpu=v5 -verify-machineinstrs -show-mc-encoding
_bk;t=1727211158841# | 1.	Running pass 'Function Pass Manager' on module '<stdin>'.
_bk;t=1727211158841# | 2.	Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@store_release_i8'
_bk;t=1727211158841# | Exception Code: 0x80000003
_bk;t=1727211158841# |  #0 0x00007ff732c3a705 (c:\ws\src\build\bin\llc.exe+0x2b4a705)
```

https://github.com/llvm/llvm-project/pull/108636