autotools: don't link with -lcrypto twice.

In case some other library with which we're linking - for example, a
version of libpcap that has rpcap-over-TLS support? - is causing us to
link with libcrypto, don't look for libcrypto ourselves.

Author: guyharris

configure.ac

@@ -857,6 +857,26 @@ AC_ARG_WITH(crypto,
 	want_libcrypto=ifavailable
 	AC_MSG_RESULT([yes, if available])
 ])
+if test "$want_libcrypto" != "no"; then
+	#
+	# Do we already *have* libcrypto, e.g. if we're using a
+	# version of libpcap that has rpcap-over-TLS support?
+	#
+	AC_MSG_CHECKING([whether we're already linking with libcrypto])
+	if $EGREP -s -q -e '-lcrypto|libcrypto' <<EOF
+$LIBS
+EOF
+	then
+		#
+		# Yes; we already *have* libcrypto, don't
+		# look for another one.
+		#
+		AC_MSG_RESULT([yes])
+		want_libcrypto=no
+	else
+		AC_MSG_RESULT([no])
+	fi
+fi
 if test "$want_libcrypto" != "no"; then
 	#
 	# Were we told where to look for libcrypto?