mosys: Enable math_unittest.

- Other unittests (io and file) require some fixing to run, will do in
separate CLs.
- Tests seem to run now w/o needing to use hacks such as building a
separate native lib (maybe meson update did help):

...
1/1 lib/math/math_unittest.c                OK       0.01 s

Ok:                    1
Expected Fail:         0
Fail:                  0
Unexpected Pass:       0
Skipped:               0
Timeout:               0
...

- Ran clang-format --style=file -i lib/math/math_unittest.c, causing a few
extra diffs.

BUG=chromium:910641
BUG=chromium:929927
TEST=sudo FEATURES='test' emerge mosys

Change-Id: I6628edd5cf892494d00bac146d0bb5e97376243f
Reviewed-on: https://chromium-review.googlesource.com/1470275
Commit-Ready: Andrew Lamb <andrewlamb@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Reviewed-by: Gregory Meinke <gmeinke@chromium.org>
6 files changed