linux-user: Run multi-threaded code on a single core

linux-user: Run multi-threaded code on a single core

Running multi-threaded code can easily expose some of the fundamental
breakages in QEMU's design. It's just not a well supported scenario.

So if we pin the whole process to a single host CPU, we guarantee that
we will never have concurrent memory access actually happen. We can still
get scheduled away at any time, so it's no complete guarantee, but apparently
it reduces the odds well enough to get my test cases to pass.

This gets Java 1.7 working for me again on my test box.

Signed-off-by: Alexander Graf <agraf@suse.de>