[llvm] [bazel] update .bazelversion to 8.0.0 (PR #119425)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

```
WARNING: WORKSPACE support will be removed in Bazel 9 (late 2025), please migrate to Bzlmod, see https://bazel.build/external/migration.
WARNING: Couldn't auto load rules or symbols, because no dependency on module/repository 'rules_android' found. This will result in a failure if there's a reference to those rules or symbols.
ERROR: /usr/local/google/home/ndesaulniers/.cache/bazel/_bazel_ndesaulniers/02cf1b716d72de9bb7498bab3b083b83/external/rules_python/python/private/reexports.bzl:37:17: name 'PyInfo' is not defined (did you mean 'CcInfo'?)
ERROR: /usr/local/google/home/ndesaulniers/.cache/bazel/_bazel_ndesaulniers/02cf1b716d72de9bb7498bab3b083b83/external/rules_python/python/private/reexports.bzl:40:24: name 'PyRuntimeInfo' is not defined
ERROR: error loading package under directory 'libc': error loading package '@@llvm-project//libc': Internal error while loading Starlark builtins: Failed to autoload external symbols: at /usr/local/google/home/ndesaulniers/.cache/bazel/_bazel_ndesaulniers/02cf1b716d72de9bb7498bab3b083b83/external/rules_python/python/py_info.bzl:18:6: compilation of module 'python/private/reexports.bzl' failed Most likely you need to upgrade the version of rules repository in the WORKSPACE file.
```
That first warning seems fine, since we have https://github.com/llvm/llvm-project/issues/55924.  Not sure yet about the rest.

https://github.com/llvm/llvm-project/pull/119425