Assume stddef.h is ubiquitious.

I can understand this was deliberate at some time but perhaps, perhaps that time has passed.

contrib/blast/blast.c

@@ -29,7 +29,7 @@
  *                      - Enable the provision of initial input to blast()
  */
 
-#include <stddef.h>             /* for NULL */
+#include <stddef.h>
 #include <setjmp.h>             /* for setjmp(), longjmp(), and jmp_buf */
 #include "blast.h"              /* prototype for blast() */
 

contrib/minizip/unzip.c

@@ -74,9 +74,9 @@
 
 #include "zlib.h"
 #include "unzip.h"
+#include <stddef.h>
 
 #ifdef STDC
-#  include <stddef.h>
 #  include <string.h>
 #  include <stdlib.h>
 #endif

contrib/minizip/zip.c

@@ -28,9 +28,9 @@
 #include <time.h>
 #include "zlib.h"
 #include "zip.h"
+#include <stddef.h>
 
 #ifdef STDC
-#  include <stddef.h>
 #  include <string.h>
 #  include <stdlib.h>
 #endif

gzguts.h

@@ -30,10 +30,7 @@
 #  define _POSIX_SOURCE
 #endif
 #include <fcntl.h>
-
-#ifdef _WIN32
-#  include <stddef.h>
-#endif
+#include <stddef.h>
 
 #if defined(__TURBOC__) || defined(_MSC_VER) || defined(_WIN32)
 #  include <io.h>

zconf.h

@@ -237,6 +237,8 @@
 #  define z_const
 #endif
 
+#include <stddef.h>
+
 #ifdef Z_SOLO
    typedef unsigned long z_size_t;
 #else
@@ -244,7 +246,6 @@
 #  if defined(NO_SIZE_T)
      typedef unsigned NO_SIZE_T z_size_t;
 #  elif defined(STDC)
-#    include <stddef.h>
      typedef size_t z_size_t;
 #  else
      typedef unsigned long z_size_t;
@@ -451,11 +452,7 @@ typedef uLong FAR uLongf;
 #  endif
 #endif
 
-#ifdef _WIN32
-#  ifndef Z_SOLO
-#    include <stddef.h>         /* for wchar_t */
-#  endif
-#endif
+#include <stddef.h>
 
 /* a little trick to accommodate both "#define _LARGEFILE64_SOURCE" and
  * "#define _LARGEFILE64_SOURCE 1" as requesting 64-bit operations, (even

zutil.h

@@ -20,11 +20,9 @@
 #endif
 
 #include "zlib.h"
+#include <stddef.h>
 
 #if defined(STDC) && !defined(Z_SOLO)
-#  if !(defined(_WIN32_WCE) && defined(_MSC_VER))
-#    include <stddef.h>
-#  endif
 #  include <string.h>
 #  include <stdlib.h>
 #endif