From a5cb6203365e0901971366445c95068f2f84529f Mon Sep 17 00:00:00 2001
From: Rene Rivera <grafikrobot@gmail.com>
Date: Tue, 8 Nov 2016 13:27:42 -0600
Subject: [PATCH] Fix BB test failures from double UPDATE_NOW calls.

---
 src/build-system.jam | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/build-system.jam b/src/build-system.jam
index ae3984621..185526c70 100644
--- a/src/build-system.jam
+++ b/src/build-system.jam
@@ -976,7 +976,10 @@ local rule should-clean-project ( project )
             # log output target. To ensure the output records all built
             # as otherwise if could execute out-of-sequence when
             # doing parallel builds.
-            UPDATE_NOW $(.out-xml) : : ignore-minus-n ;
+            if $(.out-xml)
+            {
+                UPDATE_NOW $(.out-xml) : : ignore-minus-n ;
+            }
             if $(.post-build-hook)
             {
                 $(.post-build-hook) $(ok) ;