Supports native builds on aarch64 machines.
Supports making a 64-bit build via either cross compiling, or on
aarch64 machines.
Both options require the addition of --aarch64 to the command line,
otherwise 32-bit libraries will be built.
Cross compiling requires the aarch64-linux-gnu- compile tools to
be installed (packages gcc-5-aarch64-linux-gnu and g++-aarch64-linux-gnu
on Ubuntu).
Fixes#377.
Replace hard coded -j6 in make lines for -j `nproc`
to adopt the same number of jobs as processor cores.
Discussion abounds as to whether there is a better
multiple for CPU vs I/O speeds, but it's better than
always using 6.
Changes to allow the Raspberry Pi to natively build the userland.
Assumes that any armv6l (as returned by the arch(1) command)
is a Raspberry Pi and changes the compile accordingly.
Fix for issues #2 and #79