PR#1999 broke fork detection by assuming HAVE_FORK was set for all platforms.
Include original HAVE_FORK detection logic while allowing it to be
overridden on specific platforms with -DHAVE_FORK=1 or -DHAVE_FORK=0
#include <openssl/ecdh.h>
#endif
-#if defined(OPENSSL_SYS_VMS) || defined(OPENSSL_SYS_WINDOWS) || defined(OPENSSL_SYS_MACINTOSH_CLASSIC) || defined(OPENSSL_SYS_OS2) || defined(OPENSSL_SYS_NETWARE)
-# define NO_FORK 1
-#elif HAVE_FORK
-# undef NO_FORK
+#ifndef HAVE_FORK
+# if defined(OPENSSL_SYS_VMS) || defined(OPENSSL_SYS_WINDOWS) || defined(OPENSSL_SYS_MACINTOSH_CLASSIC) || defined(OPENSSL_SYS_OS2) || defined(OPENSSL_SYS_NETWARE)
+# define HAVE_FORK 0
+# else
+# define HAVE_FORK 1
+# endif
+#endif
+
+#if HAVE_FORK
+#undef NO_FORK
#else
-# define NO_FORK 1
+#define NO_FORK
#endif
#undef BUFSIZE