cmake: safely enabling automatic testing for MSVC bitpit dynamic lib/dll

[roccoarpa]

In VS-MSVC context, executables linked to dynamic bitpit need dll of bitpit and its deps at disposal (near them or in the system path). This implies that Integration_tests/unit_tests cannot be executed automatically in this context, without copying dlls nearby them.

The most plausible solution is to provide an ad-hoc post-build command to retrieve the needed dlls and put it near the tests.
But we are open to smarter ideas.