armv8 AArch64 does not require -mfpu=neon

armv8 AArch64 does not require -mfpu=neon

-mpfu is not required on AArch64 / armv8 architecture on Linux and throws an error if present.
This PR has been tested on gcc and clang on Gentoo-64 and Raspian-64 on a Raspberry Pi 4,
as well as with a cross from Ubuntu
(`make clean && make -j build ARCH=armv8         COMP=gcc COMPILER=aarch64-linux-gnu-g++`)

fixes https://github.com/official-stockfish/Stockfish/issues/3056
closes https://github.com/official-stockfish/Stockfish/pull/3059

No functional change