+#endif
+])
+ AC_CACHE_CHECK([whether it is safe to define __EXTENSIONS__],
+ [ac_cv_safe_to_define___extensions__],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM([[
+# define __EXTENSIONS__ 1
+ ]AC_INCLUDES_DEFAULT])],
+ [ac_cv_safe_to_define___extensions__=yes],
+ [ac_cv_safe_to_define___extensions__=no])])
+ test $ac_cv_safe_to_define___extensions__ = yes &&
+ AC_DEFINE([__EXTENSIONS__])
+ AC_DEFINE([_ALL_SOURCE])
+ AC_DEFINE([_GNU_SOURCE])
+ AC_DEFINE([_POSIX_PTHREAD_SEMANTICS])
+ AC_DEFINE([_TANDEM_SOURCE])
+])# AC_USE_SYSTEM_EXTENSIONS
+
+# gl_USE_SYSTEM_EXTENSIONS
+# ------------------------
+# Enable extensions on systems that normally disable them,
+# typically due to standards-conformance issues.
+AC_DEFUN_ONCE([gl_USE_SYSTEM_EXTENSIONS],
+[
+ dnl Require this macro before AC_USE_SYSTEM_EXTENSIONS.
+ dnl gnulib does not need it. But if it gets required by third-party macros
+ dnl after AC_USE_SYSTEM_EXTENSIONS is required, autoconf 2.62..2.63 emit a
+ dnl warning: "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS".
+ dnl Note: We can do this only for one of the macros AC_AIX, AC_GNU_SOURCE,
+ dnl AC_MINIX. If people still use AC_AIX or AC_MINIX, they are out of luck.
+ AC_REQUIRE([AC_GNU_SOURCE])
+
+ AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])