Use python$EXE instead of python, for Darwin. (Patch by Tony

Lownds. (#101816)

[Note: I'm not sure that this is really the right fix.  Surely Darwin
doesn't require you to say "python.exe" everywhere???  Even Windows
doesn't!  Or am I misunderstanding the point?]

Lib/plat-generic/regen

 #! /bin/sh
 set -v
-python ../../Tools/scripts/h2py.py /usr/include/fcntl.h
-python ../../Tools/scripts/h2py.py /usr/include/sys/socket.h
-python ../../Tools/scripts/h2py.py -i '(u_long)' /usr/include/netinet/in.h
-python ../../Tools/scripts/h2py.py /usr/include/termios.h
+python$EXE ../../Tools/scripts/h2py.py /usr/include/fcntl.h
+python$EXE ../../Tools/scripts/h2py.py /usr/include/sys/socket.h
+python$EXE ../../Tools/scripts/h2py.py -i '(u_long)' /usr/include/netinet/in.h
+python$EXE ../../Tools/scripts/h2py.py /usr/include/termios.h