nix: try to make armv8.2-a / cortex-a55 optimised builds if target is aarch64

Signed-off-by: strawberry <strawberry@puppygock.gay>

nix/pkgs/main/cross-compilation-env.nix

@@ -16,6 +16,9 @@ lib.optionalAttrs stdenv.hostPlatform.isStatic {
         ++ lib.optionals
           stdenv.targetPlatform.isx86_64
           [ "-C" "target-cpu=x86-64-v2" ]
+        ++ lib.optionals
+          stdenv.targetPlatform.isAarch64
+          [ "-C" "target-cpu=cortex-a55" ] # cortex-a55 == ARMv8.2-a
         # This disables PIE for static builds, which isn't great in terms
         # of security. Unfortunately, my hand is forced because nixpkgs'
         # `libstdc++.a` is built without `-fPIE`, which precludes us from