Disable reportedly broken assembly of Sparc(64)

fixes #292
diff --git a/ChangeLog b/ChangeLog
index ef4535f..add1831 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 PolarSSL ChangeLog
 
+= Version 1.2.18 released 2015-10-xx
+
+Bugfix
+   * Fix failures in MPI on Sparc(64) due to use of bad assembly code.
+     Found by Kurt Danielson. #292
+
 = Version 1.2.17 released 2015-10-06
 
 Security