HS 2.0: Restore ifdef for DEFINE_STACK_OF in est.c

DEFINE_STACK_OF() was only introduced in OpenSSL 1.1.0 and newer, but
the ifdef directive that wrapped it was wrongly removed when cleaning
some BoringSSL definitions. Use ifdef confistently for defining and
using AttrOrOID.

Fixes: faf9c04cb5 ("Remove a host of unnecessary OPENSSL_IS_BORINGSSL ifdefs")
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>

hs20/client/est.c

@@ -218,7 +218,9 @@ typedef struct {
 	} d;
 } AttrOrOID;
 
+#if OPENSSL_VERSION_NUMBER >= 0x10100000L
 DEFINE_STACK_OF(AttrOrOID)
+#endif
 
 typedef struct {
 	int type;