configure: include stddef.h for NULL

This fixes an observed failure to detect madvise() on Linux.

To avoid similar issues, all other tests that use NULL but don't already
have stddef.h (or another header that is defined to provide NULL,
such as stdio.h, unistd.h, or time.h) are also fixed.
Signed-off-by: NScott Wood <scottwood@freescale.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

configure

@@ -1329,6 +1329,7 @@ if test "$vnc_png" != "no" ; then
 cat > $TMPC <<EOF
 //#include <stdio.h>
 #include <png.h>
+#include <stddef.h>
 int main(void) {
     png_structp png_ptr;
     png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
@@ -1513,6 +1514,7 @@ if test "$brlapi" != "no" ; then
   brlapi_libs="-lbrlapi"
   cat > $TMPC << EOF
 #include <brlapi.h>
+#include <stddef.h>
 int main( void ) { return brlapi__openConnection (NULL, NULL, NULL); }
 EOF
   if compile_prog "" "$brlapi_libs" ; then
@@ -1747,6 +1749,7 @@ if test "$linux_aio" != "no" ; then
   cat > $TMPC <<EOF
 #include <libaio.h>
 #include <sys/eventfd.h>
+#include <stddef.h>
 int main(void) { io_setup(0, NULL); io_set_eventfd(NULL, 0); eventfd(0, 0); return 0; }
 EOF
   if compile_prog "" "-laio" ; then
@@ -2127,6 +2130,7 @@ madvise=no
 cat > $TMPC << EOF
 #include <sys/types.h>
 #include <sys/mman.h>
+#include <stddef.h>
 int main(void) { return madvise(NULL, 0, MADV_DONTNEED); }
 EOF
 if compile_prog "" "" ; then
@@ -2139,6 +2143,7 @@ fi
 posix_madvise=no
 cat > $TMPC << EOF
 #include <sys/mman.h>
+#include <stddef.h>
 int main(void) { return posix_madvise(NULL, 0, POSIX_MADV_DONTNEED); }
 EOF
 if compile_prog "" "" ; then