OpenSSL: check for the SSLv2 function in configure

If no SSLv2 was detected in OpenSSL by configure, then we enforce the
OPENSSL_NO_SSL2 define as it seems some people report it not being
defined properly in the OpenSSL headers.

configure.ac

@@ -1514,7 +1514,8 @@ if test X"$OPT_SSL" != Xno; then
                     RAND_egd \
                     ENGINE_cleanup \
                     CRYPTO_cleanup_all_ex_data \
-                    SSL_get_shutdown )
+                    SSL_get_shutdown \
+                    SSLv2_client_method )
 
     dnl Make an attempt to detect if this is actually yassl's headers and
     dnl OpenSSL emulation layer. We still leave everything else believing

lib/ssluse.c

@@ -127,6 +127,11 @@
 #define HAVE_ERR_REMOVE_THREAD_STATE 1
 #endif
 
+#ifndef HAVE_SSLV2_CLIENT_METHOD
+#undef OPENSSL_NO_SSL2 /* undef first to avoid compiler warnings */
+#define OPENSSL_NO_SSL2
+#endif
+
 /*
  * Number of bytes to read from the random number seed file. This must be
  * a finite value (because some entropy "files" like /dev/urandom have