Backport revision 555794 from trunk:

Set the $prefix variable to the default prefix path if none was specified (with --prefix).

PR: 42658


git-svn-id: https://svn.apache.org/repos/asf/apr/apr-iconv/branches/1.1.x@555797 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/configure.in b/configure.in
index 8ea166b..2f6275d 100644
--- a/configure.in
+++ b/configure.in
@@ -27,6 +27,9 @@
   USE_VPATH=1
 fi
 
+dnl Default prefix path if none was specified
+test "x$prefix" = xNONE && prefix=$ac_default_prefix
+
 dnl check for APR
 API_FIND_APR