Add flag for xxhash-ffi and allow newer version (#7373)

Based on #7361

build-constraints.yaml

@@ -3659,7 +3659,7 @@ packages:
         - intset-imperative
         - lxd-client
         - lxd-client-config
-        - xxhash-ffi < 0.3 # https://github.com/commercialhaskell/stackage/issues/7361
+        - xxhash-ffi
         - zeromq4-patterns
 
     "Cliff Harvey <cs.hbar+hs@gmail.com> @BlackBrane":
@@ -8576,6 +8576,10 @@ package-flags:
 
     directory-ospath-streaming:
       os-string: false
+
+    # based on https://github.com/commercialhaskell/stackage/issues/7361
+    xxhash-ffi:
+      pkg-config: false
 # end of package-flags
 
 # Special configure options for individual packages