Hopefully fix ghc<8.2 (squash me)

Author: fgaz

Cabal/Distribution/Types/InstalledPackageInfo/FieldGrammar.hs

@@ -288,6 +288,10 @@ basicFieldGrammar = mkBasic
         -- This can be removed once we stop supporting GHC<8.8, at the
         -- condition that we keep marking main libraries as public when
         -- registering them.
-        lv' = if ln' == LMainLibName
+        MungedPackageName _ mln = n
+        lv' = if
+                -- We need to check both because on ghc<8.2 ln' will always
+                -- be LMainLibName
+                ln' == LMainLibName && mln == LMainLibName
               then LibraryVisibilityPublic
               else lv