Hide more warnings when building slycot.

Change-Id: I7eca8596dc2cf82fcba04e5b53b6559f70c50279
diff --git a/debian/usr.BUILD b/debian/usr.BUILD
index ac354cc..c66b30d 100644
--- a/debian/usr.BUILD
+++ b/debian/usr.BUILD
@@ -44,6 +44,7 @@
   ],
   copts = [
     '-Wno-error',
+    '-Wno-parentheses-equality',
   ],
   includes = [
     'lib/python3/dist-packages/numpy/f2py/src/',