We previously used 2 different versions: one from wine and one from mingw-w64. The former was used in msvcrt, the latter was statically compiled into the executable. When using MS libs, there is only one _matherr, which is statically linked into the executable and does nothing (it's not really a function for users to be called). _setusermatherror should only exist in msvcrt and not statically, which wouldn't work at all.