chore: Build for slightly more modern CPUs (#7220)

Signed-off-by: Graham King <grahamk@nvidia.com>

.cargo/config.toml

@@ -4,3 +4,12 @@
 [build]
 # tokio-console needs this
 rustflags = ["--cfg", "tokio_unstable"]
+
+# Target Haswell (2013) era+ machines. That gets us AVX-2
+[target.x86_64-unknown-linux-gnu]
+rustflags = ["-C", "target-cpu=x86-64-v3", "--cfg", "tokio_unstable"]
+
+# Target Graviton 2 / Ampere Altra + machines. NEON vector, and LSE atomics.
+[target.aarch64-unknown-linux-gnu]
+rustflags = ["-C", "target-cpu=neoverse-n1", "--cfg", "tokio_unstable"]
+