[libcxx] [llvm] [lit] Remove support for %T (PR #160028)

[James Henderson via llvm-commits]

jh7370 wrote:

What was your downstream test trying to do with `%T`?

`%T` expanded to a directory name based on the name of the test source directory and which will probably already exist. `%t` expands to a name based on the path to the test source, which probably doesn't exist. `%t.dir` is nothing special - it's just the `%t` expansion with ".dir" added to the end. You'll likely need to manually create the directory yourself in this case, e.g. something like the following at the start of the test might be worth doing:
```
# RUN: rm -rf %t.dir && mkdir %t.dir
# RUN: some-command -o %t.dir/foo
```

https://github.com/llvm/llvm-project/pull/160028