+# AS_VAR_IF(VAR, VALUE, [IF-MATCH], [IF-NOT-MATCH])
+# ----------------------------------------------------
+# Backport of autoconf-2.63b's macro.
+# Remove this macro when we can assume autoconf >= 2.64.
+m4_ifndef([AS_VAR_IF],
+[m4_define([AS_VAR_IF],
+[AS_IF([test x"AS_VAR_GET([$1])" = x""$2], [$3], [$4])])])
+