version()

[Andrej Mitrovic]

One possible workaround:

version(Windows) enum Windows = 1;
else             enum Windows = 0;
version(linux)   enum Linux = 1;
else             enum Linux = 0;
version(OSX)     enum OSX = 1;
else             enum OSX = 0;
version(Posix)   enum Posix = 1;
else             enum Posix = 0;
version(MinGW)   enum MinGW = 1;
else             enum MinGW = 0;

static if (OSX || Windows)
{
    int x;
}

void main()
{
    writeln(x);
}