[boost] [build] check __aarch64__ Aarch64

Subject: [boost] [build] check __aarch64__ Aarch64
From: Oliver Kowalke (oliver.kowalke_at_[hidden])
Date: 2015-02-24 02:23:32

Hi,
I've added an pull request for jam.h (build/engine) to set os.platform
correctly to 'ARM' on Aarch64 architecture. This is required in order to
build boost.context correctly on the64bit ARM platform.
thx,
Oliver