python38: fix build on macOS

Python 3.8 fails to build on macOS for two reasons:

* python-3.x-distutils-C++.patch fails to apply cleanly.
* An #include for <util.h> is missing, causing a build failure:

    ./Modules/posixmodule.c:6586:9: error: implicit declaration of function 'openpty' is invalid in C99
        if (openpty(&master_fd, &slave_fd, NULL, NULL, NULL) != 0)
            ^

Use the correct version of python-3.x-distutils-C++.patch, and add a
patch to #include <util.h>.

pkgs/development/interpreters/python/cpython/default.nix

@@ -100,7 +100,7 @@ in with passthru; stdenv.mkDerivation {
   ] ++ optionals isPy35 [
     # Backports support for LD_LIBRARY_PATH from 3.6
     ./3.5/ld_library_path.patch
-  ] ++ optionals isPy37 [
+  ] ++ optionals (isPy37 || isPy38) [
     # Fix darwin build https://bugs.python.org/issue34027
     (fetchpatch {
       url = https://bugs.python.org/file47666/darwin-libutil.patch;
@@ -114,7 +114,7 @@ in with passthru; stdenv.mkDerivation {
     (
       if isPy35 then
         ./3.5/python-3.x-distutils-C++.patch
-      else if isPy37 then
+      else if isPy37 || isPy38 then
         ./3.7/python-3.x-distutils-C++.patch
       else
         fetchpatch {

pkgs/development/interpreters/python/default.nix

@@ -28,6 +28,7 @@ with pkgs;
         isPy35 = pythonVersion == "3.5";
         isPy36 = pythonVersion == "3.6";
         isPy37 = pythonVersion == "3.7";
+        isPy38 = pythonVersion == "3.8";
         isPy2 = lib.strings.substring 0 1 pythonVersion == "2";
         isPy3 = lib.strings.substring 0 1 pythonVersion == "3";
         isPy3k = isPy3;