Fix for EAGAIN != EWOULDBLOCK (is there a real system?)

Fix for theoretic case EAGAIN != EWOULDBLOCK. This is not the case for
any system using glibc, or any Linux. According to google, there are some
old unix systems ... don't know if they are gone since decades.
Just check both return values and let the compiler optimize it out.

src/civetweb.c

@@ -433,6 +433,15 @@ _civet_safe_clock_gettime(int clk_id, struct timespec *t)
 #endif
 
 
+#if !defined(_WIN32)
+/* Unix might return different error codes indicating to try again.
+ * For Linux EAGAIN==EWOULDBLOCK, maybe EAGAIN!=EWOULDBLOCK is history from
+ * decades ago, but better check both and let the compile optimize it. */
+#define ERROR_TRY_AGAIN(err)                                                   \
+	(((err) == EAGAIN) || ((err) == EWOULDBLOCK) || ((err) == EINTR))
+#endif
+
+
 /********************************************************************/
 /* CivetWeb configuration defines */
 /********************************************************************/
@@ -6386,7 +6395,7 @@ push_inner(struct mg_context *ctx,
 				n = 0;
 			}
 #else
-			if (err == EWOULDBLOCK) {
+			if (ERROR_TRY_AGAIN(err)) {
 				err = 0;
 				n = 0;
 			}
@@ -6658,7 +6667,7 @@ pull_inner(FILE *fp,
 		 * blocking in close_socket_gracefully, so we can not distinguish
 		 * here. We have to wait for the timeout in both cases for now.
 		 */
-		if ((err == EAGAIN) || (err == EWOULDBLOCK) || (err == EINTR)) {
+		if (ERROR_TRY_AGAIN(err)) {
 			/* TODO (low): check if this is still required */
 			/* EAGAIN/EWOULDBLOCK:
 			 * standard case if called from close_socket_gracefully