fix(v8): set RUSTC_BOOTSTRAP=1 when using Cargo nightly features

We need to enable `-Z bindeps` to read the Chromium crates tree, but
this is not available on Cargo release builds by default. Setting
RUSTC_BOOTSTRAP overrides this behaviour.

This is technically an unstable feature, but Chromium's tooling also
uses it for the same purpose, and it's extremely unlikely to be
withdrawn.

Co-authored-by: Michaël Zasso <targos@protonmail.com>

Author: Renegade334

lib/update-v8/updateCrates.js

@@ -37,7 +37,10 @@ function enumerateTemporalDependencies() {
         {
           ignoreFailure: false,
           captureStdout: true,
-          spawnArgs: { cwd: path.join(ctx.nodeDir, chromiumCratesDir) }
+          spawnArgs: {
+            cwd: path.join(ctx.nodeDir, chromiumCratesDir),
+            env: { ...process.env, RUSTC_BOOTSTRAP: '1' }
+          }
         }
       );
       const crates = new Set();