clang-18 has a bug that causes the latest Ractor btest to crash.

It's weird that --with-gmp runs test-tool just because it needs to run
test/ruby/test_bignum.rb and spec/ruby/core/integer/*_spec.rb.

Use `nproc` rather than `nproc --all`. Because the number by the `nproc` is
different from the number by the `nproc --all` on GitHub Actions ppc64le/s390x.
This caused the `make` command runs much more jobs than the number of on-line
CPUs on these environments.
The make command ran 193 jobs in parallel for 4 on-line CPUs in GitHub Actions
ppc64le, and ran 9 jobs in parallel for 4 on-line CPUs in GitHub Actions s390x.

And this caused the high load average 34.58 on ppc64le, and 6.69 on s390x.
These values should be less than 4.0. I believe we should use the `nproc`
rather than `nproc --all`.

```
+ nproc
4
+ nproc --all
192
```

```
+ nproc
4
+ nproc --all
8
```

See https://github.com/IBM/actionspz/issues/38 for details.

Note the `--all` option in the `nproc --all` was originally added to boost CPU
in a hyper threading environment where one physical core works like two logical
cores.

https://www.intel.com/content/www/us/en/gaming/resources/hyper-threading.html

Launchable: Temporarily remove Launchable integration from Compilations workflow

Currently, Launchable is unstable, which occationally causes workflow issues. Until this problem is fixed, we'll temporary disable Launchable in the Compilations workflow.

Launchable: Terminate Launchable CLI process quickly by sending singals to a process group

Sometimes, the timeout errors occurred in Compilations workflow, this is because Launchable CLI process was not terminated correctly. To address this issue, we'll send signals to a process group.

https://github.com/ruby/ruby/actions/runs/15614867686
https://github.com/ruby/ruby/actions/runs/15662906947

Co-authored-by: Kazuhiro NISHIYAMA <zn@mbf.nifty.com>

`setup_launchable` needs to run the current shell, not in a subshell.