* configure.ac (_THREAD_SAFE): Simplify (Bug#20136).

ChangeLog

@@ -3,7 +3,7 @@
 	Better port of pthread usage to FreeBSD
 	* configure.ac (ac_func_list): Omit pthread_sigmask, since
 	we check for that ourselves rather than relying on gnulib.
-	(HAVE_PTHREAD, LIB_PTHREAD, _THREAD_SAFE): Port better to FreeBSD,
+	(HAVE_PTHREAD, LIB_PTHREAD): Port better to FreeBSD,
 	by also checking for pthread_create, pthread_self, pthread_sigmask.
 	Tighten the test for pthread_atfork while we're at it.
 	Fixes: bug#20136

configure.ac

@@ -2234,7 +2234,7 @@ if test "$ac_cv_header_pthread_h" && test "$opsys" != "mingw32"; then
       hpux* | sol*)
 	AC_DEFINE([_REENTRANT], 1,
 	  [Define to 1 if your system requires this in multithreaded code.]);;
-      aix4-2 | darwin | freebsd)
+      aix4-2)
 	AC_DEFINE([_THREAD_SAFE], 1,
 	  [Define to 1 if your system requires this in multithreaded code.]);;
     esac