return a list of libraries to link against.

def get_libraries():
    '''return a list of libraries to link against.'''
    # Note that this list does not include libcsamtools.so as there are
    # numerous name conflicts with libchtslib.so.
    dirname = os.path.abspath(os.path.join(os.path.dirname(__file__)))
    pysam_libs = ['libctabixproxies',
                  'libcfaidx',
                  'libcsamfile',
                  'libcvcf',
                  'libcbcf',
                  'libctabix']
    if pysam.config.HTSLIB == "builtin":
        pysam_libs.append('libchtslib')

    so = sysconfig.get_config_var('SO')
    return [os.path.join(dirname, x + so) for x in pysam_libs]