Disable reportedly broken assembly of Sparc(64)

fixes #292
diff --git a/ChangeLog b/ChangeLog
index 928012f..71fdd7b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,7 +7,8 @@
      begin properly ignored. Found by mancha and Kasom Koht-arsa, #308
    * Fix build error with configurations where ECDHE-PSK is the only key
      exchange. Found and fix provided by Chris Hammond. #270
-
+   * Fix failures in MPI on Sparc(64) due to use of bad assembly code.
+     Found by Kurt Danielson. #292
 
 = mbed TLS 1.3.14 released 2015-10-06