distutils: pass -rpath on macOS when requested

Fix -R option of build_ext for macOS (darwin)

Resolves this old bug against distutils that expired due to PIP 632:
https://bugs.python.org/issue36353

Applies patch originally submitted to CPython:
python/cpython#12418

distutils/unixccompiler.py

@@ -233,8 +233,7 @@ def runtime_library_dir_option(self, dir):
         # we use this hack.
         compiler = os.path.basename(sysconfig.get_config_var("CC"))
         if sys.platform[:6] == "darwin":
-            # MacOSX's linker doesn't understand the -R flag at all
-            return "-L" + dir
+            return "-Wl,-rpath," + dir
         elif sys.platform[:7] == "freebsd":
             return "-Wl,-rpath=" + dir
         elif sys.platform[:5] == "hp-ux":