clang: Allow Travis CI builds to succeed

.travis.yml

@@ -60,6 +60,12 @@ matrix:
       env: GCC_VER=5 TARGET=debug.nounity CLANG_VER=3.6
       addons: *ao_clang36
 
+  # Temporary workaround while the llvm apt repository is down.
+  # TODO: REMOVE THIS if/when clang builds become reliable again.
+  allow_failures:
+    - env: GCC_VER=5 TARGET=debug CLANG_VER=3.6
+    - env: GCC_VER=5 TARGET=debug.nounity CLANG_VER=3.6
+
 cache:
   directories:
   - $BOOST_ROOT