[llvmlinux] Unmatching Arch String for Aarch64/arm64

[zhaoshiz at codeaurora.org]

Hi,

Please direct me to the right place for filing a bug if needed.

It seems linux kernel use arm64 as the arch string for 64-bit ARM. But
llvm uses aarch64. As a result, when using native clang, build fails by
hitting this error: "Your native clang does not have arm64 support".

I tried to substitute arm64 with aarch64 in clang-native.mk but had no luck.

Can any one shed some light?

Thanks,
Zhaoshi