ansible: install llvm-toolset for building V8

[richardlau]

When building with clang, the V8 CI needs other tools such as llvm-ar found in llvm-toolset on RHEL.

[richardlau]

e.g. https://ci.nodejs.org/job/richardlau-node-test-commit-v8-linux/742/nodes=rhel8-s390x,v8test=v8test/console

18:01:54 [293/2303] rm -f obj/libv8_libbase.a && "/usr/bin/llvm-ar" -T -S -r -c -D obj/libv8_libbase.a @"obj/libv8_libbase.a.rsp"
18:01:54 FAILED: obj/libv8_libbase.a 
18:01:54 rm -f obj/libv8_libbase.a && "/usr/bin/llvm-ar" -T -S -r -c -D obj/libv8_libbase.a @"obj/libv8_libbase.a.rsp"
18:01:54 /bin/sh: /usr/bin/llvm-ar: No such file or directory
18:01:54 ninja: build stopped: subcommand failed.

Test CI (nodejs/node#59805 + nodejs/node#59893): https://ci.nodejs.org/job/richardlau-node-test-commit-v8-linux/746/nodes=rhel8-s390x,v8test=v8test/ ✔️