- Enable parallel builds by default (and allow using environment
variables to override `make` variables)
- Hopefully we can get rid of this once we have Meson
- Set `GTEST_BRIEF=1`
- This only shows failed tests, instead of listing every test on its
own line.
```
$ GTEST_BRIEF=1 make check
[==========] 328 tests from 15 test suites ran. (37 ms total)
[ PASSED ] 328 tests.
```
Change-Id: Id8103a8f24a9681be2be87e1b4df6fd5fdd7e4fd