cargo-config: use Rust's front-end parallel compilation

Use the recommended configuration that enables the front-end parallel
compilation for faster builds

Signed-off-by: Arnaldo Garcia Rincon <[email protected]>

Author: arnaldo2792

.cargo/config.toml

@@ -1,2 +1,8 @@
 [unstable]
 bindeps = true
+
+[build]
+# This is the recommended configuration that yields the
+# best results:
+#  - https://blog.rust-lang.org/2023/11/09/parallel-rustc.html
+rustflags = ["-Z", "threads=8"]