configure: Move "experimental" warning to bottom

to make it more promiment

configure.ac

@@ -435,12 +435,7 @@ fi
 ### Check for --enable-experimental if necessary
 ###
 
-if test x"$enable_experimental" = x"yes"; then
-  AC_MSG_NOTICE([******])
-  AC_MSG_NOTICE([WARNING: experimental build])
-  AC_MSG_NOTICE([Experimental features do not have stable APIs or properties, and may not be safe for production use.])
-  AC_MSG_NOTICE([******])
-else
+if test x"$enable_experimental" = x"no"; then
   if test x"$set_asm" = x"arm32"; then
     AC_MSG_ERROR([ARM32 assembly is experimental. Use --enable-experimental to allow.])
   fi
@@ -508,3 +503,10 @@ if test x"$print_msan_notice" = x"yes"; then
   echo "  MemorySanitizer detected, tried to add -fno-sanitize-memory-param-retval to SECP_CFLAGS"
   echo "  to avoid false positives in ctime_tests. Pass --disable-ctime-tests to avoid this."
 fi
+
+if test x"$enable_experimental" = x"yes"; then
+  echo
+  echo "WARNING: Experimental build"
+  echo "  Experimental features do not have stable APIs or properties, and may not be safe for"
+  echo "  production use."
+fi