package/rocksdb: fix build without dlfcn.h

Fixes:
 - http://autobuild.buildroot.org/results/04c5afff034d8d71d11b95c998e3156292852de6

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/rocksdb/rocksdb.mk

@@ -70,6 +70,7 @@ endif
 ifeq ($(BR2_STATIC_LIBS),y)
 ROCKSDB_BUILD_TARGETS += static_lib
 ROCKSDB_INSTALL_TARGETS += install-static
+ROCKSDB_EXTRA_CXXFLAGS += -DROCKSDB_NO_DYNAMIC_EXTENSION
 else ifeq ($(BR2_SHARED_LIBS),y)
 ROCKSDB_BUILD_TARGETS += shared_lib
 ROCKSDB_INSTALL_TARGETS += install-shared