tool/gocross: remove GOROOT to ensure correct toolchain use

go(1) repsects GOROOT if set, but tool/go / gocross-wrapper.sh are explicitly intending to use our toolchain. We don't need to set GOROOT, just unset it, and then go(1) handles the rest.

Updates tailscale/corp#26717

Signed-off-by: James Tucker <james@tailscale.com>

tool/gocross/gocross-wrapper.sh

@@ -133,6 +133,12 @@ fi
 
 repo_root="${BASH_SOURCE%/*}/../.."
 
+# Some scripts/package systems set GOROOT even though they should only be
+# setting $PATH. Stop them from breaking builds - go(1) respects GOROOT and
+# so if it is left on here, compilation units depending on our Go fork will
+# fail (such as those which depend on our net/ patches).
+unset GOROOT
+
 # gocross is opt-in as of 2025-06-16. See tailscale/corp#26717
 # and comment above in this file.
 if [ "${TS_USE_GOCROSS:-}" != "1" ]; then