Add support for z13 processor

Add support for z13 processor

The z13 supports some useful instructions that can be exploited
by the JIT. Most notably the compare-and-branch instructions can
reduce a two instruction sequence to one. The load-and-add command
eliminates the more complex compare-and-swap sequence.

The z13 also supports three operand instructions dst,src1,src2
which eliminate checks and loads for instructions like add and subtract.

The unaligned.cs test has been changed to cater for big-endian platforms.
For s390x only, the --trace option will result in a file per thread
being created rather than the traces being written to stdout and
sometimes intermixing incomplete trace entries.