Support Apple Silicon Mac

[cielavenir]

As the further work of #162 , in https://github.com/cielavenir/isa-l/tree/fix_mach , I was able to assemble aarch64 code for Apple Silicon Mac.
I needed slight modification but the assembled Android binary still works.
However, although I believe the (modified) Android code path and Apple Silicon Mac code path should be the same, Apple Silicon code path raises Bus error.

I suppose Apple Silicon Mac demand will be rising.

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How I tested my work:

make -f Makefile.unx CC=arm64-apple-darwin-gcc AR=arm64-apple-darwin-ar arch=aarch64 host_cpu=aarch64 DEFINES="-fno-stack-check" lib programs/igzip -j8

where

arm64-apple-darwin-gcc
XCODE=$HOME/Downloads/Xcode.app
SYSROOT=$XCODE/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk
$XCODE/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -isysroot $SYSROOT -arch arm64 "$@"

arm64-apple-darwin-ar
XCODE=$HOME/Downloads/Xcode.app
SYSROOT=$XCODE/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk
$XCODE/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar "$@"

[cielavenir]

I was able to fix the bus error here, so now it will be converted into PR.