在 Mac OSX 上从源代码编译某些包时，出现以下 iconv 错误：
Undefined symbols for architecture x86_64:
"_iconv", referenced from:
"_iconv_close", referenced from:
"_iconv_open", referenced from:
或者我得到：
Undefined symbols for architecture x86_64:
"_libiconv", referenced from:
"_libiconv_open", referenced from:
"_libiconv_close", referenced from:
为什么会发生这种情况，我该如何解决这种依赖性，或者更一般地说，弄清楚发生了什么以及如何解决它？