[clang] [Coroutines][Test] Specify target triple in coro-elide-thinlto (PR #90549)

[Wei Wang via cfe-commits]

apolloww wrote:

This should make Buildbot failure like https://lab.llvm.org/buildbot/#/builders/38/builds/19079 to go away

```
warning: linking module 'coro-elide-caller.o': Linking two modules of different target triples: 'coro-elide-callee.o' is 'x86_64-unknown-linux' whereas 'coro-elide-caller.o' is 'hexagon-unknown-unknown-elf'
```

https://github.com/llvm/llvm-project/pull/90549