define NULL as nullptr when used in C++11 or later

This should be safer for casting and more compatible with existing code
bases that wrongly assume it must be defined as a pointer.

include/locale.h

@@ -7,7 +7,9 @@ extern "C" {
 
 #include <features.h>
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)

include/stddef.h

 #ifndef _STDDEF_H
 #define _STDDEF_H
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)

include/stdio.h

@@ -25,7 +25,9 @@ extern "C" {
 
 #include <bits/alltypes.h>
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)

include/stdlib.h

@@ -7,7 +7,9 @@ extern "C" {
 
 #include <features.h>
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)

include/string.h

@@ -7,7 +7,9 @@ extern "C" {
 
 #include <features.h>
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)

include/time.h

@@ -7,7 +7,9 @@ extern "C" {
 
 #include <features.h>
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)

include/unistd.h

@@ -15,7 +15,9 @@ extern "C" {
 #define SEEK_CUR 1
 #define SEEK_END 2
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)

include/wchar.h

@@ -38,7 +38,9 @@ extern "C" {
 #define WCHAR_MIN (-1-0x7fffffff+L'\0')
 #endif
 
-#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0L
 #else
 #define NULL ((void*)0)