[clang-tools-extra] [clangd] Use TargetOpts from preamble when building ASTs (PR #88381)

[via cfe-commits]

zibi2 wrote:

@kadircet FYI, I noticed our Linux on Power down stream build failues related to this change. The upstream builds are also faling see https://lab.llvm.org/buildbot/#/builders/57/builds/34415 for example.

```
ld.lld: error: undefined symbol: llvm::Triple::getArchName() const
>>> referenced by ParsedASTTests.cpp
```

This symbol is define in `Triple.cpp.o` which is part of `libLLVMTargetParser.a`  which is not built. Not building this archive and a bunch of others is the root of the problem. 

Can you have a look and try to fix it?
Thanks, Zibi.

https://github.com/llvm/llvm-project/pull/88381