Vector Pascal Compiler Code

Correct the interface to compileUnit in MultiThreadPascal, and alter
the make file to make sure that dependence on multithread pascal is captured.

Attempt to get the 64 bit C code generator working reliably on x86 currently fails many tests

Fix a bug which was affecting the combination of loop invariants and register
caching of local variables.
The interpretation of the optimisation flags has been changed to give
finer control over different optimisations.
The help text for vpc -h has been updated

fixing some poor code generation for pixel to real inter working and also taking into account how we need weight 1 for labels now since they have to be loaded into a register

add packed conversion of int to float