lxml 3.6.3 fails to build on Mac OS X 10.11.6

[mario_grgic]

I am on Mac OS X 10.11.6 and Python 3.5.2 (currently have lxml versoin 3.6.1 installed):

Python : sys.version_info(major=3, minor=5, micro=2, releaselevel='final', serial=0)
lxml.etree : (3, 6, 1, 0)
libxml used : (2, 9, 2)
libxml compiled : (2, 9, 2)
libxslt used : (1, 1, 28)
libxslt compiled : (1, 1, 28)

Trying to upgrade to 3.6.3 fails when linking:

    gcc -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/usr/local/ssl/include -I/usr/include/libxml2 -Isrc/lxml/includes -I/Library/Frameworks/Python.framework/Versions/3.5/include/python3.5m -c src/lxml/lxml.etree.c -o build/temp.macosx-10.11-x86_64-3.5/src/lxml/lxml.etree.o -w -flat_namespace
    gcc -bundle -undefined dynamic_lookup -L/usr/local/ssl/lib build/temp.macosx-10.11-x86_64-3.5/src/lxml/lxml.etree.o -lxslt -lexslt -lrt -lxml2 -lz -lm -o build/lib.macosx-10.11-x86_64-3.5/lxml/etree.cpython-35m-darwin.so
    ld: library not found for -lrt
    clang: error: linker command failed with exit code 1 (use -v to see invocation)
    error: command 'gcc' failed with exit status 1

From what I understand librt is available on Linux only and it does not exist on Mac OS X.