Explicit block for conditional.
Remove odd each_in_mask 'optimization'

Deal with that if/when it's an issue.
Mark value_t as final.
Add explicit ctors for value_t.
Remove use of value_t::make, fix stack resize bug.

Stack would be resized to be one too small for the requested location.
Remove use of make in test code.
Remove value_t::make.
Replace use of int32_t with value_t in relocations.

Not pretty, but it potentially avoids some loss of data in relocations
and doesn't tie it integer values only.
Remove unused build script.
Add primitive conditional loop support to asm2bc.

Syntax:
  for [COND] {
      /* instructions */
  }

Results in:
  @__for_start_label:
      CONDTEST
      jump @__for_end_label 0x1
      /* instructions */
      jump @__for_start_label 0x1
  @__for_end_label:
      /* done */

So basically it's just an if conditional with a jump back to the start
at the end of the block.
Fix up test.asm