Darwin8 does not have _SC_NPROCESSORS_ONLN defined.

OK for trunk & 4.6?
Iain

Index: gcc/ada/adaint.c
===================================================================
--- gcc/ada/adaint.c	(revision 178554)
+++ gcc/ada/adaint.c	(working copy)
@@ -2460,7 +2460,10 @@ __gnat_number_of_cpus (void)
    int cores = 1;

  #if defined (linux) || defined (sun) || defined (AIX) \
-    || (defined (__alpha__)  && defined (_osf_)) || defined (__APPLE__)
+    || (defined (__alpha__)  && defined (_osf_)) \
+    || (defined (__APPLE__) \
+        && defined (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) \
+        && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1050)
    cores = (int) sysconf (_SC_NPROCESSORS_ONLN);

  #elif (defined (__mips) && defined (__sgi))