[CVS ci] PCC 1-3

[Leopold Toetsch]

Parrot now has basic PCC (Parrot Calling Convention) support inside the
PIR assembler.
1) no fancy stuff like register renumbering
2) only the upper half of all registers are preserved currently

TODO:
- tests
- more tests
- docs
- still more tests
- optimize register usage
- tail call optimizations
- check which registers have to be preserved over sub calls
- preserve only necessary register sets
- allocate regs that have not to be preserved in the lower half of regs
- if too many regs have to be preserved then emit saveall/restoreall
including save/restore return values around restoreall.

Register allocation now starts at #16 for each set, giving 16 preserved
registers for sub calls. That should be enough for first tests.

SYNOPSIS:
s. languages/imcc/docs/calling_conventions.pod

Have fun,
leo