Failure is a part of life, and we just have to deal with it and move on. After several hours of trying to compile the aarch64 gcc cross compiler on macOS myself, I have given it up for now. I will continue development and testing in 32bit. I'll just compile and test on linux for aarch64 when a major version has been released.

I got as far as getting a binary for the g++ compiler, but using it with circle results in:

  CPP   actled.o
'armv8-a+crc' is not a recognized processor for this target (ignoring processor)
'armv8-a+crc' is not a recognized processor for this target (ignoring processor)
/var/folders/q1/0jsxyqlx6jl_592pvc_z3lx00000gn/T//ccLAjiBh.s:1:2: error: unknown directive
        .arch armv8-a+crc
        ^
/var/folders/q1/0jsxyqlx6jl_592pvc_z3lx00000gn/T//ccLAjiBh.s:10:2: error: unknown directive
        .type   _ZN7CActLEDC2Eb, %function
        ^
/var/folders/q1/0jsxyqlx6jl_592pvc_z3lx00000gn/T//ccLAjiBh.s:17:16: error: brackets expression not supported on this target
        stp     x29, x30, [sp, -48]!
                          ^
/var/folders/q1/0jsxyqlx6jl_592pvc_z3lx00000gn/T//ccLAjiBh.s:21:2: error: unknown use of instruction mnemonic without a size suffix
        mov     x29, sp
        ^
/var/folders/q1/0jsxyqlx6jl_592pvc_z3lx00000gn/T//ccLAjiBh.s:25:2: error: invalid instruction mnemonic 'adrp'
        adrp    x2, .LANCHOR0
        ^~~~

 This is the procedure that finally gave me a (non-working) g++ binary:

#download aarch64 gcc arm compiler source (https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-a/downloads)
#extract and cd into directory

./contrib/download-prerequisites

mkdir build && cd build

../configure --build=x86_64-build_apple-darwin19.5.0 --host=x86_64-build_apple-darwin19.5.0 --target=aarch64-none-elf --prefix=/Users/nick/Downloads/aarch64/aarch64-none-elf --with-local-prefix=/Users/nick/Downloads/aarch64/aarch64-none-elf/aarch64-none-elf --with-gnu-as --with-gnu-ld --disable-libstdcxx --without-headers --with-newlib --enable-threads=no --disable-shared --disable-__cxa_atexit --disable-libffi --disable-libgomp --disable-libmudflap --disable-libmpx --disable-libssp --disable-libquadmath --disable-libquadmath-support --enable-lto --enable-target-optspace --disable-nls --disable-multilib --enable-languages=c,c++

make -j 8

stdlibc++-v3 gave me a lot of problems when compiling that I could not figure out, so I tried to compile g++ without libsdtcxx. I figure that is the root cause of all subsequent problems. Anyway, I wanted to share my workflow just in case someone else wants to have a stab at it. 

For the record, compiling the c compiler with the configure parameters below works, it's the c++ compiler that's giving me a hard time.

download gcc arm source
extract

./contrib/download-prerequisites

mkdir build && cd build

../configure --build=x86_64-build_apple-darwin19.5.0 --host=x86_64-build_apple-darwin19.5.0 --target=aarch64-none-elf --prefix=/Users/nick/Downloads/aarch64/aarch64-none-elf --with-local-prefix=/Users/nick/Downloads/aarch64/aarch64-none-elf/aarch64-none-elf --without-headers --with-newlib --enable-threads=no --disable-shared --disable-__cxa_atexit --disable-libgomp --disable-libmudflap --disable-libmpx --disable-libssp --disable-libquadmath --disable-libquadmath-support --enable-lto --enable-target-optspace --disable-nls --disable-multilib --enable-languages=c

make -j 8

make install-strip