fix DummyRNG in tests for clang builds

When trying to build all tests on clang12, I get the error:

/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/random:3645:51: error: call to non-static member function without an object argument
    const size_t __logR = __log2<uint64_t, _URNG::max() - _URNG::min() + uint64_t(1)>::value;

It found some codes with similar issues when compiling on clang. I was able to fix this compiling issues with the changes in this PR.

If it doesn't change the outcome on other systems, I would be grateful for merging this.