Mixin to optimise builds for Raspberry Pi 4

index.yaml

mixin:
  - tune-pi4.mixin

tune-pi4.mixin

{
    "build": {
        "tune-pi4": {
            "cmake-args": [
                "-DCMAKE_C_FLAGS=-march=armv8-a+crc -mtune=cortex-a72 -O3",
                "-DCMAKE_CXX_FLAGS=-march=armv8-a+crc -mtune=cortex-a72 -O3"
            ]
        }
    }
}