Fix BVGauss unit tests. (#3142)

Fix BVGauss unit tests. (#3142)

pass_bv_gauss_white.h included bv_gauss.cpp to test the functions in the
anonymous namespace, which resulted in ODR (one definition rule)
violations reported by ASAN.

This commit exposes the functionality required in the unit tests as
private static members of the BVGauss class. Since this is a white unit
test, we can access private members in the tests.