When building with VS2017 the compiler shows some warnings which is
undesirable.
The compiler rightly complains about declarations which hide older ones
which are trivially fixed.
Finally only POD types should be passed to variadic functions which is
why the String should be converted to c_str().
Relying on the current undefined behavior is a bad idea as it can change
with compilers and compiler versions.
Closesjp9000/obs-studio#902
26c28b4502