[2/2] The sparse byte code writer.

To test the writer:

$ ./test-write linearize.c
export syms 29 internal 72 import 47
struct instruction * size 349524
struct entrypoint * size 2280
struct basic_block * size 39248
pseudo_t size 118632
struct pseudo_user * size 0
struct asm_constraint * size 0
struct symbol * size 358608
struct asm_rules * size 0
struct multijmp * size 1344
struct expression * size 4064
struct ident * size 12596
struct string * size 0
char * size 0
char * (stream) size 191
struct ptr_list * size 114948
toalsize 995359

It generate linearize.b file.

Some internal detail:

traverse.c is responsible for traverse the pointer in an object.
It don't actually convert the pointer. It delegates the actual convertion
to the caller. The reader and writer can share the same traverse
code to convert the pointer to index, index back to pointer.