Index: include/private/misc.h
===================================================================
--- include/private/misc.h	(revision 3509)
+++ include/private/misc.h	(working copy)
@@ -45,7 +45,6 @@
 /**
  * ffsl helpers.
  */
-
 #ifdef __GNUC__
 
 #  if (__GNUC__ >= 4) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 4))
@@ -303,7 +302,7 @@
 hwloc_weight_long(unsigned long w)
 {
 #if HWLOC_BITS_PER_LONG == 32
-#if (__GNUC__ >= 4) || ((__GNUC__ == 3) && (__GNUC_MINOR__) >= 4)
+#if ((__GNUC__ >= 4) || ((__GNUC__ == 3) && (__GNUC_MINOR__) >= 4)) && HWLOC_HAVE_GCC_BUILTIN != 0
 	return __builtin_popcount(w);
 #else
 	unsigned int res = (w & 0x55555555) + ((w >> 1) & 0x55555555);
@@ -313,7 +312,7 @@
 	return (res & 0x0000FFFF) + ((res >> 16) & 0x0000FFFF);
 #endif
 #else /* HWLOC_BITS_PER_LONG == 32 */
-#if (__GNUC__ >= 4) || ((__GNUC__ == 3) && (__GNUC_MINOR__) >= 4)
+#if ((__GNUC__ >= 4) || ((__GNUC__ == 3) && (__GNUC_MINOR__) >= 4))  && HWLOC_HAVE_GCC_BUILTIN != 0
 	return __builtin_popcountll(w);
 #else
 	unsigned long res;
Index: config/hwloc_internal.m4
===================================================================
--- config/hwloc_internal.m4	(revision 3509)
+++ config/hwloc_internal.m4	(working copy)
@@ -65,6 +65,11 @@
                   AS_HELP_STRING([--disable-pci],
                                  [Disable the PCI device discovery using libpci]))
 
+    # GCC-Builtin?
+    AC_ARG_ENABLE([gcc_builtin],
+                  AS_HELP_STRING([--disable-gcc-builtin], 
+		                 [Disable the use of gcc __builtin_ functions, when gcc is used]))
+
 ])dnl
 
 #-----------------------------------------------------------------------
Index: config/hwloc.m4
===================================================================
--- config/hwloc.m4	(revision 3509)
+++ config/hwloc.m4	(working copy)
@@ -590,6 +590,15 @@
     fi
     HWLOC_CFLAGS="$HWLOC_CFLAGS $HWLOC_XML_CFLAGS"    
 
+    # GCC-Builtin support
+    if test "x$enable_gcc_builtin" != "xno"; then
+        AC_DEFINE([HWLOC_HAVE_GCC_BUILTIN], [1], [Define to 1 if you want GCC __builtin, when available.])
+        AC_SUBST([HWLOC_HAVE_GCC_BUILTIN], [1])
+    else
+        AC_DEFINE([HWLOC_HAVE_GCC_BUILTIN], [0], [Define to 0 if you do not want GCC __builtin, when available.])
+        AC_SUBST([HWLOC_HAVE_GCC_BUILTIN], [0])
+    fi
+
     # Setup HWLOC's C, CPP, and LD flags, and LIBS
     AC_SUBST(HWLOC_REQUIRES)
     AC_SUBST(HWLOC_CFLAGS)
@@ -679,6 +688,7 @@
         AM_CONDITIONAL([HWLOC_HAVE_CAIRO], [test "x$enable_cairo" != "xno"])
         AM_CONDITIONAL([HWLOC_HAVE_XML], [test "x$enable_xml" != "xno"])
         AM_CONDITIONAL([HWLOC_HAVE_LIBPCI], [test "x$enable_pci" != "xno"])
+        AM_CONDITIONAL([HWLOC_HAVE_GCC_BUILTIN], [test "x$enable_gcc_builtin" != "xno"])
         AM_CONDITIONAL([HWLOC_HAVE_SET_MEMPOLICY], [test "x$enable_set_mempolicy" != "xno"])
         AM_CONDITIONAL([HWLOC_HAVE_MBIND], [test "x$enable_mbind" != "xno"])
         AM_CONDITIONAL([HWLOC_HAVE_BUNZIPP], [test "x$BUNZIPP" != "xfalse"])