r8brain-free resampling library from https://github.com/avaneev/r8brain-free-src
version 7.1.
 *  The example program, DLL and "other" folder, PFFFT sources and logo file
    have been removed.
 *  ARM64 Clang-cl build has been fixed in r8bbase.h.
 *  All modifications have been marked with // OpenMPT.
 *  No further local changes have been made.
 *  For building, premake is used to generate Visual Studio project files. See
    ../build/premake/ for details.
