I double confirmed with our engineer for this question.
Actually, we are compiling on a 64-bit machine and the compiler is also 64-bit as github showing: https://github.com/raspberrypi/tools/tree/master/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64
The command -m64 is not recognized in this compiler.
Please provide the compiler name or the complete correct compiler command on your platform so we can double check this.
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