For non-Windows platforms which includes Cygwin default the value of
BOOST_NOWIDE_USE_FILEBUF_REPLACEMENT to that of BOOST_NOWIDE_USE_WCHAR_OVERLOADS.
Also allow overwriting the value of BOOST_NOWIDE_USE_WCHAR_OVERLOADS.
Especially with C++17 it may be useful to not use the custom filebuf.
Hence give users more control over this, although this risks ODR violations.
Flamefire