fix(v8): restore Linux sandbox artifact builds

Keep non-Windows rusty-v8 consumers on the resolved 147.4.0 source-built graph. Avoid mixing LLVM's default libc++ headers into rusty-v8's custom libc++ build, propagate that configuration to external C++ deps, and export the musl-specific libc++ define through the shared header target.

Also make checksum validation follow the remaining prebuilt asset version while the source-build migration is in progress.

Co-authored-by: Codex <noreply@openai.com>

MODULE.bazel

@@ -10,6 +10,7 @@ single_version_override(
     module_name = "llvm",
     patch_strip = 1,
     patches = [
+        "//patches:llvm_rusty_v8_custom_libcxx.patch",
         "//patches:llvm_windows_symlink_extract.patch",
     ],
 )