Build LLVM using Bazel instead of CMake

[PiotrSikora]

LLVM can be built using Bazel (see: https://github.com/llvm/llvm-project/tree/main/utils/bazel), which would be cacheable.

Currently, WAMR JIT and WAVM tests are building LLVM using CMake, which isn't cacheable and results in multi-hour CI runs.

cc @mpwarres

[lum1n0us]

If someone help to sync the "removing WAVM" PR from envoy project, WAMR can jump to pre-built LLVM binraries. Then there is no need to build LLVM.