The relevant part of the log is:
:info:build png-write.c:285:21: error: incomplete definition of type 'struct png_struct_def'
:info:build if (setjmp (png_ptr->jmpbuf)) {
:info:build ~~~~~~~^
:info:build /opt/local/include/png.h:857:16: note: forward declaration of 'struct png_struct_def'
:info:build typedef struct png_struct_def png_struct;
:info:build ^
:info:build png-write.c:373:27: error: incomplete definition of type 'struct png_struct_def'
:info:build if (!n) longjmp (png_ptr->jmpbuf, 1);
:info:build ~~~~~~~^
:info:build /opt/local/include/png.h:857:16: note: forward declaration of 'struct png_struct_def'
:info:build typedef struct png_struct_def png_struct;
:info:build ^
So this is the usual symptom of incompatibility with libpng 1.5. We need to update the port to a newer version or patch this problem ourselves.