Add graph coloring register allocator.
Refactored linear allocator into separate liveness annotation and allocation stages.
Added graph coloring allocator, use -fregs-graph to enable.
New dump flags are
-ddump-asm-native -- output of cmm -> native transform.
-ddump-asm-liveness -- code annotated with register liveness info
-ddump-asm-coalesce -- output of register move coalescing
(this is a separate pass when using the coloring allocator)
(this could change in the future)
-ddump-asm-regalloc -- code after register allocation
-ddump-asm-regalloc-stages -- blocks after each build/spill stage of coloring allocator
-ddump-asm-conflicts -- a global register liveness graph in graphviz format
The new register allocator will allocate some registers, but it's not
quite ready for prime-time yet. The spill code generator needs some work...