Fail test if test failed
https://github.com/imneme/pcg-cpp/pull/100

--- a/test-high/run-tests.sh
+++ b/test-high/run-tests.sh
@@ -94,5 +94,6 @@ else
         echo All tests except tests awkward tests with 128-bit math succceed.
     else
         echo ERROR: Some tests failed.
+        exit 1
     fi
 fi