Floating point fixups

See merge request !165

Brute-forcing this at present. Would be better to wrap this
conditionally for the architecture.

Add floating point support

See merge request !164

Misc exception handling fixups

See merge request !163

Fixes for grant maps and others

See merge request !162

When mapping one (from) virtual address range to another (to) virtual
address range, be mindful of which mapper type to use for each range.

Before this, the same mapper type was used for both ranges. This meant
that if from and to were different (as in not both kernel virtual
addresses or user virtual addresses) then it would appear that either
from or to was not mapped previously and the kernel would panic.

This makes asserts on VirtualAddressType equality possible.

Wip clone and misc fixes

See merge request !161

At present these are done 'wholesale' without any regard for x86_64.
That needs to change eventually.

FIXME: Explain the magic numbers here later.

No CLONE_STACK functionality yet.

Was using the incorrect USER_TLS_OFFSET instead of USER_TCB_OFFSET. In
any case, this is better done in process::clone.

So we can more clearly see when things go wrong.

Pagetabletype and misc fixes

See merge request !158

Misc fixes

See merge request !160