binaryen: link fails for 10.7 thru 10.12: undefined symbol std::bad_optional_access destructor

[mascguy (Christopher Nielsen)]

Details from buildbots:

[ 86%] Linking CXX shared library lib/libbinaryen.dylib
/opt/local/bin/cmake -E cmake_link_script CMakeFiles/binaryen.dir/link.txt --verbose=ON
Undefined symbols for architecture x86_64:
  "std::bad_optional_access::~bad_optional_access()", referenced from:
      __ZNSt3__127__throw_bad_optional_accessB7v160006Ev in TranslateEH.cpp.o
  "vtable for std::bad_variant_access", referenced from:
      __ZNSt3__126__throw_bad_variant_accessB7v160006Ev in possible-contents.cpp.o
      __ZNSt3__126__throw_bad_variant_accessB7v160006Ev in type-updating.cpp.o
      __ZNSt3__126__throw_bad_variant_accessB7v160006Ev in param-utils.cpp.o
      __ZNSt3__126__throw_bad_variant_accessB7v160006Ev in ConstantFieldPropagation.cpp.o
      __ZNSt3__126__throw_bad_variant_accessB7v160006Ev in Directize.cpp.o
      __ZNSt3__126__throw_bad_variant_accessB7v160006Ev in GlobalStructInference.cpp.o
      __ZNSt3__126__throw_bad_variant_accessB7v160006Ev in GUFA.cpp.o
      ...
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for std::bad_optional_access", referenced from:
      __ZNSt3__127__throw_bad_optional_accessB7v160006Ev in TranslateEH.cpp.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64

But given that the port builds successfully for 10.6 - even 32-bit - this should be fixable.