use `-undefined dynamic_lookup` option for Darwin
use `-undefined dynamic_lookup` option for Darwin

fix an error in generating shared object

```
+ gcc -shared -o libctrpercolator.so percolator.o
Undefined symbols for architecture x86_64:
  "_ctr_build_number_from_float", referenced from:
      _ctr_percolator_new in percolator.o
  "_ctr_build_string", referenced from:
      _ctr_percolator_brew in percolator.o
      _ctr_percolator_add_coffee_water in percolator.o
      _ctr_percolator_new in percolator.o
      _begin in percolator.o
  "_ctr_internal_cast2number", referenced from:
      _ctr_percolator_add_coffee_water in percolator.o
  "_ctr_internal_create_func", referenced from:
      _begin in percolator.o
  "_ctr_internal_create_object", referenced from:
      _ctr_percolator_new in percolator.o
  "_ctr_internal_object_add_property", referenced from:
      _begin in percolator.o
  "_ctr_internal_object_find_property", referenced from:
      _ctr_percolator_brew in percolator.o
  "_ctr_internal_object_set_property", referenced from:
      _ctr_percolator_brew in percolator.o
      _ctr_percolator_add_coffee_water in percolator.o
      _ctr_percolator_new in percolator.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```

but I got another error...

```
% ./ctr tests/test0117.ctr
Let's make a nice cup of coffee!
[1]    59021 segmentation fault  ./ctr tests/test0117.ctr
```

gabordemooij/citrine,takano32/citrine,gabordemooij/citrine,gabordemooij/citrine,takano32/citrine,takano32/citrine