make patchcheck depends on the interpreter and modules being built to work correctly but the make target doesn't have this expressed. This simple patch will fix it and adds well under a second of latency for me.

cpython.hg$ make patchcheck
./python ./Tools/scripts/patchcheck.py
Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
Failed to import the site module
Traceback (most recent call last):
  File "/home/robertc/work/cpython.hg/Lib/site.py", line 555, in <module>
    main()
  File "/home/robertc/work/cpython.hg/Lib/site.py", line 541, in main
    known_paths = addusersitepackages(known_paths)
  File "/home/robertc/work/cpython.hg/Lib/site.py", line 281, in addusersitepackages
    user_site = getusersitepackages()
  File "/home/robertc/work/cpython.hg/Lib/site.py", line 257, in getusersitepackages
    user_base = getuserbase() # this will also set USER_BASE
  File "/home/robertc/work/cpython.hg/Lib/site.py", line 247, in getuserbase
    USER_BASE = get_config_var('userbase')
  File "/home/robertc/work/cpython.hg/Lib/sysconfig.py", line 582, in get_config_var
    return get_config_vars().get(name)
  File "/home/robertc/work/cpython.hg/Lib/sysconfig.py", line 531, in get_config_vars
    _init_posix(_CONFIG_VARS)
  File "/home/robertc/work/cpython.hg/Lib/sysconfig.py", line 403, in _init_posix
    from _sysconfigdata import build_time_vars
ImportError: No module named '_sysconfigdata'
Makefile:1640: recipe for target 'patchcheck' failed
make: *** [patchcheck] Error 1