The phone is one SoC, 4x Cortex-A520 + 4x Cortex-A720, and the package is
built for nothing else, so build for it: -march=armv8.6-a+fp16fml+aes+sha3+sm4
-mtune=cortex-a720 instead of the generic Armv8 baseline. That is gcc's own
-march=native expansion on the phone, re-based on armv8.6-a so clang can
express the same set; 8.6 is the highest level whose mandatory set the phone
exposes (8.7 would assume WFxT, 9.x SVE2 - neither is in its hwcaps, and
SVE2 code would SIGILL). Same string as the fp6-img aports and kernel.