kunit: tool: add support for building kernel with additional threads

Allows the user to specify how many threads to be used for building the
kernel as part of building and running tests.

Google-Bug-Id: 131440297
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Change-Id: If1c10b7e122b5863b7e07f467c7008d3e6397336
2 files changed