Hi,

When emulating a mixed 32/64 bit Qemu target CPUs it's easy to confuse
the TCGv size, passing 32 bit TCGv to a function expecting a 64 bit
one and vice versa. This patch adds a run time sanity check for TCGv
sizes.

Because a 32 bit Qemu host does not really use 64 bit TCGvs, the patch
is only functional on a 64 bit host. Of course also a pure 32 bit Qemu
target is not likely to suffer from TCGv size confusion.

Some use cases are not covered yet. Comments?