discover nanosleep() availability in configure

config/s-templ.h

@@ -130,6 +130,9 @@
 /* Define HAS_SYS_SELECT_H if /usr/include/sys/select.h exists
    and should be included before using select(). */
 
+#define HAS_NANOSLEEP
+/* Define HAS_NANOSLEEP if you have nanosleep(). */
+
 #define HAS_SYMLINK
 
 /* Define HAS_SYMLINK if you have symlink() and readlink() and lstat(). */

configure

@@ -1230,6 +1230,11 @@ if sh ./hasgot select && \
   has_select=yes
 fi
 
+if sh ./hasgot nanosleep ; then
+  inf "nanosleep() found."
+  echo "#define HAS_NANOSLEEP" >> s.h
+fi
+
 if sh ./hasgot symlink readlink lstat;  then
   inf "symlink() found."
   echo "#define HAS_SYMLINK" >> s.h

otherlibs/unix/sleep.c

@@ -31,7 +31,7 @@ CAMLprim value unix_sleep(value duration)
 {
   double d = Double_val(duration);
   if (d <= 0.0) return Val_unit;
-#if _POSIX_C_SOURCE >= 199309L
+#if defined(HAS_NANOSLEEP)
   {
     struct timespec t;
     int ret;