[clang] [llvm] [clang][SPIR-V] Implement -fspv-preserve-interface (PR #196404)

[Diego Novillo via cfe-commits]

dnovillo wrote:

> > > @bogner thanks for the review. Would you be able to submit the PR for me? I don't have write access to the repo. Thanks.
> > 
> > 
> > ~I'll do it.~
> > After the rebase son hlsl tests failed. @dnovillo could you check this ?
> > The windows failure look related to this PR.
> 
> Will do. Thanks for the heads up.

I looked at the failures but I could not find a relation to my PR:

1. macOS has a failure in `OffloadTest-clang-mtl :: WaveOps/WaveReadLaneAt.index.test` that I can't see being caused by the flag:

```
Function: main: error: I8 can only be used as immediate value for intrinsic or as i8* via bitcast by lifetime intrinsics.
note: at '%21 = getelementptr inbounds [3 x i8], [3 x i8]* @switch.table.main, i32 0, i32 %20' in block '#1' of function 'main'.
Function: main: error: I8 can only be used as immediate value for intrinsic or as i8* via bitcast by lifetime intrinsics.
note: at '%22 = load i8, i8* %21, align 1' in block '#1' of function 'main'.
Function: main: error: I8 can only be used as immediate value for intrinsic or as i8* via bitcast by lifetime intrinsics.
note: at '%23 = zext i8 %22 to i32' in block '#1' of function 'main'.
Validation failed.
clang-dxc: error: dxv command failed with exit code 1 (use -v to see invocation)
```

2. The windows bot is getting an sccache timeout:

```
sccache: error: Timed out waiting for server startup
sccache: error: Timed out waiting for server startup. Maybe the remote service is unreachable?
Run with SCCACHE_LOG=debug SCCACHE_NO_DAEMON=1 to get more information
Process completed with exit code 2.
```

Not sure how to deal with these failures.

https://github.com/llvm/llvm-project/pull/196404