+# This definition of AC_USE_SYSTEM_EXTENSIONS is stolen from CVS
+# Autoconf. Perhaps we can remove this once we can assume Autoconf
+# 2.62 or later everywhere, but since CVS Autoconf mutates rapidly
+# enough in this area it's likely we'll need to redefine
+# AC_USE_SYSTEM_EXTENSIONS for quite some time.
+
+# If autoconf reports a warning
+# warning: AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS
+# or warning: AC_RUN_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS
+# the fix is
+# 1) to ensure that AC_USE_SYSTEM_EXTENSIONS is never directly invoked
+# but always AC_REQUIREd,
+# 2) to ensure that for each occurrence of
+# AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
+# or
+# AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+# the corresponding gnulib module description has 'extensions' among
+# its dependencies. This will ensure that the gl_USE_SYSTEM_EXTENSIONS
+# invocation occurs in gl_EARLY, not in gl_INIT.
+
+# AC_USE_SYSTEM_EXTENSIONS