+
+ // Both POSIX and Single UNIX Specification say that this variable must
+ // exist but not that it must be declared anywhere and, indeed, it's not
+ // declared in several common systems (some BSDs, Solaris with native CC)
+ // so we (re)declare it ourselves to deal with these cases. However we do
+ // not do this under MSW where there can be DLL-related complications, i.e.
+ // the variable might be DLL-imported or not. Luckily we don't have to
+ // worry about this as all MSW compilers do seem to define it in their
+ // standard headers anyhow so we can just rely on already having the
+ // correct declaration. And if this turns out to be wrong, we can always
+ // add a configure test checking whether it is declared later.
+#ifndef __WINDOWS__