Allow ghc[-gmp] to discover integer-simple: https://bugs.gentoo.org/790467
--- a/blaze-textual.cabal
+++ b/blaze-textual.cabal
@@ -39,7 +39,6 @@ flag native
 flag integer-simple
   description: use integer-simple instead of integer-gmp
   default: False
-  manual: True
 
 library
   exposed-modules: