bpo-35081: Add pycore_ prefix to internal header files (GH-10263)

* Rename Include/internal/ header files:

  * pyatomic.h -> pycore_atomic.h
  * ceval.h -> pycore_ceval.h
  * condvar.h -> pycore_condvar.h
  * context.h -> pycore_context.h
  * pygetopt.h -> pycore_getopt.h
  * gil.h -> pycore_gil.h
  * hamt.h -> pycore_hamt.h
  * hash.h -> pycore_hash.h
  * mem.h -> pycore_mem.h
  * pystate.h -> pycore_state.h
  * warnings.h -> pycore_warnings.h

* PCbuild project, Makefile.pre.in, Modules/Setup: add the
  Include/internal/ directory to the search paths of header files.
* Update includes. For example, replace #include "internal/mem.h"
  with #include "pycore_mem.h".
diff --git a/Modules/makesetup b/Modules/makesetup
index c7b0a60..bf5ca39 100755
--- a/Modules/makesetup
+++ b/Modules/makesetup
@@ -110,7 +110,7 @@
 	rulesf="@rules.$$"
 	trap 'rm -f $rulesf' 0 1 2 3
 	echo "
-# Rules appended by makedepend
+# Rules appended by makesetup
 " >$rulesf
 	DEFS=
 	BUILT=