No functional changes, as measured by identical spec2k asm output.

1. Use early "return" and "continue" to reduce "if" nesting.

2. Reflow comments to 80 columns (instead of presumably 79).

3. Add some BuildDefs::dump() tests to reduce translator code size.

BUG= none
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/1448773002 .