CFI improvements to the AArch64 fiber implementation (#4195)

Now the fiber implementation on AArch64 authenticates function
return addresses and includes the relevant BTI instructions, except
on macOS.

Also, change the locations of the saved FP and LR registers on the
fiber stack to make them compliant with the Procedure Call Standard
for the Arm 64-bit Architecture.

Copyright (c) 2022, Arm Limited.

.github/workflows/main.yml

@@ -211,8 +211,6 @@ jobs:
             gcc: aarch64-linux-gnu-gcc
             qemu: qemu-aarch64 -L /usr/aarch64-linux-gnu
             qemu_target: aarch64-linux-user
-            # FIXME(#3183) shouldn't be necessary to specify this
-            qemu_flags: -cpu max,pauth=off
           - os: ubuntu-latest
             target: s390x-unknown-linux-gnu
             gcc_package: gcc-s390x-linux-gnu
@@ -251,7 +249,7 @@ jobs:
         # Configure Cargo for cross compilation and tell it how it can run
         # cross executables
         upcase=$(echo ${{ matrix.target }} | awk '{ print toupper($0) }' | sed 's/-/_/g')
-        echo CARGO_TARGET_${upcase}_RUNNER=${{ runner.tool_cache }}/qemu/bin/${{ matrix.qemu }} ${{ matrix.qemu_flags }} >> $GITHUB_ENV
+        echo CARGO_TARGET_${upcase}_RUNNER=${{ runner.tool_cache }}/qemu/bin/${{ matrix.qemu }} >> $GITHUB_ENV
         echo CARGO_TARGET_${upcase}_LINKER=${{ matrix.gcc }} >> $GITHUB_ENV
 
         # QEMU emulation is not always the speediest, so total testing time