title: How to detect if errno_t is defined?
body: <p>I'm compiling code using gcc that comes from Visual C++ 2008. The code is using errno_t, but in some versions of gcc headers including <code>&lt;errno.h&gt;</code> doesn't define the type. How do I detect if the type is defined? Is there a define that signals that the type was defined? In the case it isn't defined I'd like to provide the typedef to let the code compile correctly on all platforms.</p>