package/libcutl: fix build with gcc 11

package/libcutl: fix build with gcc 11

Add -std=c++11 to fix the following build failure with gcc 11:

In file included from shared-ptr/base.cxx:5:
../cutl/shared-ptr/base.hxx:34:41: error: ISO C++17 does not allow dynamic exception specifications
   34 | operator new (std::size_t, cutl::share) throw (std::bad_alloc);
      |                                         ^~~~~

Fixes:
 - http://autobuild.buildroot.org/results/60a39d402a0d051c92aa11421b7a14f7729a0380

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>