The error when installing lxml with pip

lxml_error

Installing collected packages: lxml
  Running setup.py install for lxml
    /System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/dist.py:267: UserWarning: Unknown distribution option: 'bugtrack_url'
      warnings.warn(msg)
    Building lxml version 3.3.3.
    Building without Cython.
    Using build configuration of libxslt 1.1.28
    Building against libxml2/libxslt in the following directory: //anaconda/lib
    ...
    clang: error: linker command failed with exit code 1 (use -v to see invocation)
    error: command 'cc' failed with exit status 1

...
clang: error: linker command failed with exit code 1 (use -v to see invocation)

error: command 'cc' failed with exit status 1