bpo-40422: Move _Py_closerange to fileutils.c (GH-22680)

This API is relatively lightweight and organizationally, given that it's
used by multiple modules, it makes sense to move it to fileutils.

Requires making sure that _posixsubprocess is compiled with the appropriate
Py_BUIILD_CORE_BUILTIN macro.
diff --git a/Modules/Setup b/Modules/Setup
index 470bf6b..87f3a7c 100644
--- a/Modules/Setup
+++ b/Modules/Setup
@@ -226,7 +226,7 @@
 #termios termios.c	# Steen Lumholt's termios module
 #resource resource.c	# Jeremy Hylton's rlimit interface
 
-#_posixsubprocess _posixsubprocess.c  # POSIX subprocess module helper
+#_posixsubprocess  -DPy_BUILD_CORE_BUILTIN _posixsubprocess.c  # POSIX subprocess module helper
 
 # Multimedia modules -- off by default.
 # These don't work for 64-bit platforms!!!