[clang] [llvm] [llvm] Enable TLSDESC by default on Fuchsia targets (PR #124990)

[Paul Kirth via llvm-commits]

ilovepi wrote:

### Merge activity

* **Jan 30, 1:23 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/124990).


https://github.com/llvm/llvm-project/pull/124990