python: enable makeflags option

It mostly worked, except for some ln failures in make install due to not
being able to create a broken symlink to a file to be created later.
Fixed by making the make rule that ln's depend on the rule that creates
the files.

python/960-fix-parallel-make.patch

@@ -0,0 +1,11 @@
+--- Python-3.8.5/Makefile.pre.in.orig	2020-08-14 12:32:57.031236300 -0700
++++ Python-3.8.5/Makefile.pre.in	2020-08-14 12:33:19.884645300 -0700
+@@ -1256,7 +1256,7 @@
+ 			$(DESTDIR)$(BINDIR)/python$(VERSION)$(EXE); \
+ 	fi
+ 
+-bininstall: altbininstall
++bininstall: altbininstall commoninstall
+ 	if test ! -d $(DESTDIR)$(LIBPC); then \
+ 		echo "Creating directory $(LIBPC)"; \
+ 		$(INSTALL) -d -m $(DIRMODE) $(DESTDIR)$(LIBPC); \