configure: correctly detect bignum

Building with bignum is currently not possible, since we're checking
ol_with_tls against a value it is never assigned in any case.

Since bignum is from openssl, and openssl is the preferred TLS
implementation, if the bignum headers are found, it means we do have
TLS and it is opensl.

So, keep the check for the bignum header, but check against ol_link_tls
which means that openssl is enabled when we find the bignum headers.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

diff -durN openldap-2.4.40.orig/configure openldap-2.4.40/configure
--- openldap-2.4.40.orig/configure	2014-09-19 03:48:49.000000000 +0200
+++ openldap-2.4.40/configure	2015-01-25 18:44:54.216879362 +0100
@@ -23431,7 +23431,7 @@
 
 	if test "$ac_cv_header_openssl_bn_h" = "yes" &&
 		test "$ac_cv_header_openssl_crypto_h" = "yes" &&
-		test "$ol_with_tls" = "found" ; then
+		test "$ol_link_tls" = "yes" ; then
 		ol_with_mp=bignum
 
 $as_echo "#define USE_MP_BIGNUM 1" >>confdefs.h
diff -durN openldap-2.4.40.orig/configure.in openldap-2.4.40/configure.in
--- openldap-2.4.40.orig/configure.in	2014-09-19 03:48:49.000000000 +0200
+++ openldap-2.4.40/configure.in	2015-01-25 18:44:37.628676446 +0100
@@ -2383,7 +2383,7 @@
 	AC_CHECK_HEADERS(openssl/crypto.h)
 	if test "$ac_cv_header_openssl_bn_h" = "yes" &&
 		test "$ac_cv_header_openssl_crypto_h" = "yes" &&
-		test "$ol_with_tls" = "found" ; then
+		test "$ol_link_tls" = "yes" ; then
 		ol_with_mp=bignum
 		AC_DEFINE(USE_MP_BIGNUM,1,[define to use OpenSSL BIGNUM for MP])
 	elif test $ol_with_mp = bignum ; then