Build failure due to missing ldl library

I get the following build error (sdk 2.0):

g++ -Wl,--as-needed -Wl,--no-undefined -static-libgcc -shared -Wl,-Bsymbolic -Wl,-soname=libvamp-hostsdk.so.3 -ldl -o src/libvamp-hostsdk.so src/vamp-hostsdk/PluginHostAdapter.o src/vamp-hostsdk/RealTime.o src/vamp-hostsdk/PluginBufferingAdapter.o src/vamp-hostsdk/PluginChannelAdapter.o src/vamp-hostsdk/PluginInputDomainAdapter.o src/vamp-hostsdk/PluginLoader.o src/vamp-hostsdk/PluginSummarisingAdapter.o src/vamp-hostsdk/PluginWrapper.o
src/vamp-hostsdk/PluginLoader.o: In function `_VampHost::Vamp::HostExt::PluginLoader::Impl::loadLibrary(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
/usr/src/rpm/BUILD/vamp-plugin-sdk-2.0/src/vamp-hostsdk/PluginLoader.cpp:522: undefined reference to `dlopen'
/usr/src/rpm/BUILD/vamp-plugin-sdk-2.0/src/vamp-hostsdk/PluginLoader.cpp:525: undefined reference to `dlerror'
src/vamp-hostsdk/PluginLoader.o: In function `_VampHost::Vamp::HostExt::PluginLoader::Impl::lookupInLibrary(void*, char const*)':
/usr/src/rpm/BUILD/vamp-plugin-sdk-2.0/src/vamp-hostsdk/PluginLoader.cpp:547: undefined reference to `dlsym'
src/vamp-hostsdk/PluginLoader.o: In function `_VampHost::Vamp::HostExt::PluginLoader::Impl::unloadLibrary(void*)':
/usr/src/rpm/BUILD/vamp-plugin-sdk-2.0/src/vamp-hostsdk/PluginLoader.cpp:537: undefined reference to `dlclose'

I could only resolve them by changing Makefile.in:
$(SDK_DYNAMIC): $(SDK_OBJECTS) $(API_HEADERS) $(SDK_HEADERS)
$(CXX) $(LDFLAGS) $(SDK_DYNAMIC_LDFLAGS) -o $@ $(SDK_OBJECTS) @LIBS@

$(HOSTSDK_DYNAMIC): $(HOSTSDK_OBJECTS) $(API_HEADERS) $(HOSTSDK_HEADERS)
$(CXX) $(LDFLAGS) $(HOSTSDK_DYNAMIC_LDFLAGS) -o $@ $(HOSTSDK_OBJECTS) @LIBS@

(@LIBS@ was added)

Regards