layer.conf: remove '-mbranch-protection=standard' globally on aarch64

[quaresmajose]

On aarch64 the handling of runtime exception is broken when build with clang.
There is currently a fix for libcxx on the layer but it is not enough and this same fix needs to be applied globally.

First fix attempt just include libcxx:
#963
#968

Remaining reported issue:
#998

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[kraj]

LGTM