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/Setup b/Modules/Setup
index fb16698..c180463 100644
--- a/Modules/Setup
+++ b/Modules/Setup
@@ -101,29 +101,29 @@
 # This only contains the minimal set of modules required to run the
 # setup.py script in the root of the Python source tree.
 
-posix -DPy_BUILD_CORE posixmodule.c	# posix (UNIX) system calls
+posix -DPy_BUILD_CORE -I$(srcdir)/Include/internal posixmodule.c # posix (UNIX) system calls
 errno errnomodule.c			# posix (UNIX) errno values
 pwd pwdmodule.c				# this is needed to find out the user's home dir
 					# if $HOME is not set
 _sre _sre.c				# Fredrik Lundh's new regular expressions
 _codecs _codecsmodule.c			# access to the builtin codecs and codec registry
 _weakref _weakref.c			# weak references
-_functools -DPy_BUILD_CORE _functoolsmodule.c   # Tools for working with functions and callable objects
+_functools -DPy_BUILD_CORE -I$(srcdir)/Include/internal _functoolsmodule.c   # Tools for working with functions and callable objects
 _operator _operator.c	        	# operator.add() and similar goodies
 _collections _collectionsmodule.c	# Container types
 _abc _abc.c				# Abstract base classes
 itertools itertoolsmodule.c		# Functions creating iterators for efficient looping
 atexit atexitmodule.c			# Register functions to be run at interpreter-shutdown
-_signal -DPy_BUILD_CORE signalmodule.c
+_signal -DPy_BUILD_CORE -I$(srcdir)/Include/internal signalmodule.c
 _stat _stat.c				# stat.h interface
-time -DPy_BUILD_CORE timemodule.c	# -lm # time operations and variables
-_thread -DPy_BUILD_CORE _threadmodule.c	# low-level threading interface
+time -DPy_BUILD_CORE -I$(srcdir)/Include/internal timemodule.c	# -lm # time operations and variables
+_thread -DPy_BUILD_CORE -I$(srcdir)/Include/internal _threadmodule.c	# low-level threading interface
 
 # access to ISO C locale support
 _locale _localemodule.c  # -lintl
 
 # Standard I/O baseline
-_io -DPy_BUILD_CORE -I$(srcdir)/Modules/_io _io/_iomodule.c _io/iobase.c _io/fileio.c _io/bytesio.c _io/bufferedio.c _io/textio.c _io/stringio.c
+_io -DPy_BUILD_CORE -I$(srcdir)/Include/internal -I$(srcdir)/Modules/_io _io/_iomodule.c _io/iobase.c _io/fileio.c _io/bytesio.c _io/bufferedio.c _io/textio.c _io/stringio.c
 
 # faulthandler module
 faulthandler faulthandler.c