Sync with upstream yasm 1.2.0 source tarball.

This is in preparation for updating to yasm 1.3.0. The update to 1.2.0
did not fully sync with the source tarball, which means yasm 1.3.0 must
either be updated piecemeal or be an unreviewable mess. The goal here is
to separate the irrelevant unreviewable mess from the relevant and
hopefully less unreviewable mess.

This CL was created by replacing this directory with the 1.2.0 tarball,
looking through the diff, and recovering our patches.

To review, look at the file list and verify that nothing is touched that
would affected Chromium. By my count, there is:

Mkfiles/* - random build files for other buildsystems
*/tests/* - test files
modules/preprocs/gas/ - a module that we forgot to enable but presumably
    don't use.
* - miscellaenous goop

Bug: 753886
Change-Id: Id2204b0f358bd3ae2bf44afc75254fc4b2088f4e
167 files changed