src: fix compiler warning

The warning is:

../src/util.h:65:11: warning: inline function
'node::Calloc<unsigned char>' is not defined [-Wundefined-inline]
inline T* Calloc(size_t n);
          ^
../src/aliased_buffer.h:41:15: note: used here
    buffer_ = Calloc<NativeT>(count);

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines