HIPSPV toolchain not tested on macOS CI — missing aligned allocation case crashes compiler

## Summary

The HIPSPV toolchain (`spirv64` / `spirv64-unknown-chipstar` targets) has no macOS CI test coverage, which allowed a crash to go undetected: `alignedAllocMinVersion()` in `AlignedAllocation.h` hits `llvm_unreachable` for `Triple::ChipStar` because it has no `case` in the switch.

## How to reproduce

On macOS, compile any C++17 code targeting chipStar:

```
clang++ -target x86_64-apple-darwin --offload=spirv64-unknown-chipstar test.hip
```

The Darwin host toolchain's `addClangTargetOptions()` checks aligned allocation support for the device triple's OS, calls `alignedAllocMinVersion(Triple::ChipStar)`, and crashes.

## Root cause

- `hipspv-toolchain.hip` is only marked `UNSUPPORTED: system-windows, system-cygwin` — it's not unsupported on macOS, but no macOS CI bot runs it
- The `ChipStar` OS type was added to the `Triple` enum but `AlignedAllocation.h` was not updated with a corresponding `case`
- Linux CI doesn't catch this because the Linux host toolchain doesn't check aligned allocation availability

## Suggestion

1. Add `case llvm::Triple::ChipStar:` to `alignedAllocMinVersion()` (fix already prepared in https://github.com/llvm/llvm-project/pull/183991 and CHIP-SPV fork)
2. Consider adding macOS test coverage for HIPSPV targets to catch similar issues in the future (e.g., a macOS bot that runs `check-clang-driver` with the SPIR-V backend enabled)

## Affected files

- `clang/include/clang/Basic/AlignedAllocation.h` — missing switch case
- `clang/lib/Driver/ToolChains/HIPSPV.cpp` — `HostTC->addClangTargetOptions()` delegation exposes the crash on macOS

Start with clang/include/clang/Basic/AlignedAllocation.h and inspect alignedAllocMinVersion(), then trace the call from clang/lib/Driver/ToolChains/HIPSPV.cpp. Review hipspv-toolchain.hip and the check-clang-driver coverage described in the issue. Done means ChipStar no longer reaches the crash and macOS HIPSPV coverage exercises this path.

Written by the indexing model from the issue text.