The macro itself is broken in autoconf-2.13 but this is caused by newer kernels
etc rather than anything else. Very, very few packages use autoconf-2.13, let
alone AC_FUNC_GETLOADAVG, so not going to worry about it much.

Do as Fedora and Debian do and skip the test for it.

https://bugs.gentoo.org/406723
https://bugs.gentoo.org/677926
--- a/testsuite/autoconf.s/syntax.exp
+++ b/testsuite/autoconf.s/syntax.exp
@@ -2,7 +2,8 @@
 
 send_user "Checking for syntax errors in the specific tests...\n"
 set script {s/^AC_DEFUN(\([^,]*\).*/\1/p}
-set macros [exec sed -n $script $srcdir/../acspecific.m4]
+# XXX: AC_FUNC_GETLOADAVG skipped for bug #406723, bug #677926
+set macros [exec sed -n $script $srcdir/../acspecific.m4 | grep -v AC_FUNC_GETLOADAVG]
 
 foreach mac $macros {
     if { [string match "*F77*" "$mac"] && [catch {exec which g77} ignore_output] } then {