Handle EWOULDBLOCK as EAGAIN if they happen to be different.

Fixes bug 7935.  Reported by 'oftc_must_be_destroyed'.

changes/bug7935

@@ -0,0 +1,4 @@
+  o Minor features (portability):
+    - Work correctly on unix systems where EAGAIN and EWOULDBLOCK are
+      separate error codes--or at least, don't break for that reason.
+      Fixes bug 7935. Reported by "oftc_must_be_destroyed".

src/common/compat.h

@@ -53,6 +53,7 @@
 #endif
 
 #include <stdio.h>
+#include <errno.h>
 
 #if defined (WINCE)
 #include <fcntl.h>
@@ -538,10 +539,14 @@ int tor_socket_errno(tor_socket_t sock);
 const char *tor_socket_strerror(int e);
 #else
 #define SOCK_ERRNO(e) e
+#if EAGAIN == EWOULDBLOCK
 #define ERRNO_IS_EAGAIN(e)           ((e) == EAGAIN)
+#else
+#define ERRNO_IS_EAGAIN(e)           ((e) == EAGAIN || (e) == EWOULDBLOCK)
+#endif
 #define ERRNO_IS_EINPROGRESS(e)      ((e) == EINPROGRESS)
 #define ERRNO_IS_CONN_EINPROGRESS(e) ((e) == EINPROGRESS)
-#define ERRNO_IS_ACCEPT_EAGAIN(e)    ((e) == EAGAIN || (e) == ECONNABORTED)
+#define ERRNO_IS_ACCEPT_EAGAIN(e)    (ERRNO_IS_EAGAIN(e) || (e) == ECONNABORTED)
 #define ERRNO_IS_ACCEPT_RESOURCE_LIMIT(e) \
   ((e) == EMFILE || (e) == ENFILE || (e) == ENOBUFS || (e) == ENOMEM)
 #define ERRNO_IS_EADDRINUSE(e)       ((e) == EADDRINUSE)

src/ext/eventdns.c

@@ -368,7 +368,11 @@ error_is_eagain(int err)
 #define CLOSE_SOCKET(x) closesocket(x)
 #else
 #define last_error(sock) (errno)
+#if EAGAIN != EWOULDBLOCK
+#define error_is_eagain(err) ((err) == EAGAIN || (err) == EWOULDBLOCK)
+#else
 #define error_is_eagain(err) ((err) == EAGAIN)
+#endif
 #define CLOSE_SOCKET(x) close(x)
 #endif