bpo-45434: pyport.h no longer includes <stdlib.h> (GH-28914)

Include <stdlib.h> explicitly in C files.

Python.h includes <wchar.h>.

Python/dtoa.c

@@ -119,6 +119,7 @@
 
 #include "Python.h"
 #include "pycore_dtoa.h"
+#include <stdlib.h>               // exit()
 
 /* if PY_NO_SHORT_FLOAT_REPR is defined, then don't even try to compile
    the following code */

Python/errors.c

@@ -15,12 +15,13 @@ extern char *strerror(int);
 #endif
 #endif
 
+#include <ctype.h>
 #ifdef MS_WINDOWS
-#include <windows.h>
-#include <winbase.h>
+#  include <windows.h>
+#  include <winbase.h>
+#  include <stdlib.h>             // _sys_nerr
 #endif
 
-#include <ctype.h>
 
 #ifdef __cplusplus
 extern "C" {

Python/fileutils.c

@@ -3,6 +3,7 @@
 #include "pycore_runtime.h"       // _PyRuntime
 #include "osdefs.h"               // SEP
 #include <locale.h>
+#include <stdlib.h>               // mbstowcs()
 
 #ifdef MS_WINDOWS
 #  include <malloc.h>

Python/initconfig.c

@@ -10,7 +10,9 @@
 #include "pycore_pystate.h"       // _PyThreadState_GET()
 
 #include "osdefs.h"               // DELIM
+
 #include <locale.h>               // setlocale()
+#include <stdlib.h>               // getenv()
 #if defined(MS_WINDOWS) || defined(__CYGWIN__)
 #  ifdef HAVE_IO_H
 #    include <io.h>

Python/preconfig.c

@@ -4,7 +4,9 @@
 #include "pycore_initconfig.h"    // _PyArgv
 #include "pycore_pymem.h"         // _PyMem_GetAllocatorName()
 #include "pycore_runtime.h"       // _PyRuntime_Initialize()
+
 #include <locale.h>               // setlocale()
+#include <stdlib.h>               // getenv()
 
 
 /* Forward declarations */

Python/pylifecycle.c

@@ -16,6 +16,7 @@
 #include "pycore_traceback.h"     // _Py_DumpTracebackThreads()
 
 #include <locale.h>               // setlocale()
+#include <stdlib.h>               // getenv()
 
 #if defined(__APPLE__)
 #include <mach-o/loader.h>

Python/pystrhex.c

@@ -1,8 +1,8 @@
 /* Format bytes as hexadecimal */
 
 #include "Python.h"
-#include "pycore_strhex.h"       // _Py_strhex_with_sep()
-
+#include "pycore_strhex.h"        // _Py_strhex_with_sep()
+#include <stdlib.h>               // abs()
 
 static PyObject *_Py_strhex_impl(const char* argbuf, const Py_ssize_t arglen,
                                  const PyObject* sep, int bytes_per_sep_group,