[RaphaelFakhri]

Fixes #527.

When cargo build runs from a git hook, git has already exported GIT_DIR and related variables. The build script inherits them, so git init and git apply in OUT_DIR run against the caller's repository instead of the copied BoringSSL sources. When the hook runs in a worktree, git init writes core.bare = true into the main checkout's config, and git commands in the main checkout fail with fatal: this operation must be run in a work tree.

Changes

• Add a git_command() helper in boring-sys/build/main.rs that removes the variables listed by git rev-parse --local-env-vars.
• Use it for all three git invocations (submodule update, init, apply).

Testing

The build script has no test harness, so this was checked with a script that simulates a hook in a consumer worktree:

git init consumer/main && git -C consumer/main commit --allow-empty -m init
git -C consumer/main worktree add ../wt
GIT_DIR=$(git -C consumer/wt rev-parse --absolute-git-dir) cargo build -p boring-sys
git -C consumer/main config --get core.bare
git -C consumer/main status

• Before: core.bare is true and git status in the main checkout fails.
• After: core.bare is false, git status works, and the patches are applied in OUT_DIR/boringssl, which now gets its own .git.

cargo fmt --all -- --check, cargo clippy -p boring-sys --all-targets and cargo test -p boring (300 + 9 + 39 passed) are clean.

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