build: add option to disable tests

When building for a product, tests are not needed.

Besides, one test requires a C++ compiler, which is not always
available.

So, add an option to configure to disable building tests altogether.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>