address win32 build issues

- Replace external -DOPENSSL/-DPKCS11CRYPTO with properly AC_DEFINEd
  HAVE_OPENSSL/HAVE_PKCS11
- Don't enforce the crypto provider from platform.h, just from dst_api.c
  and configure scripts

lib/dns/tests/dh_test.c

@@ -30,7 +30,7 @@
 
 #include "dnstest.h"
 
-#if defined(OPENSSL) && !defined(PK11_DH_DISABLE)
+#if HAVE_OPENSSL && !defined(PK11_DH_DISABLE)
 
 ATF_TC(isc_dh_computesecret);
 ATF_TC_HEAD(isc_dh_computesecret, tc) {
@@ -83,7 +83,7 @@ ATF_TC_BODY(untested, tc) {
  * Main
  */
 ATF_TP_ADD_TCS(tp) {
-#if defined(OPENSSL) && !defined(PK11_DH_DISABLE)
+#if HAVE_OPENSSL && !defined(PK11_DH_DISABLE)
 	ATF_TP_ADD_TC(tp, isc_dh_computesecret);
 #else
 	ATF_TP_ADD_TC(tp, untested);