Don't warn about functions not emitted

If a function is used by a template but this template is not
instantiated, the function will still be defined in the header
of a module but it won't be callable because it is in an anonymous
namespace and thus we get a warning.

This only happens in Clang; GCC consider functions referenced from
templates as used.

fixup! Don't warn about functions not emitted

opm/core/simulator/initState_impl.hpp

@@ -40,6 +40,8 @@ namespace Opm
     namespace
     {
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunneeded-internal-declaration"
         // Find the cells that are below and above a depth.
         // TODO: add 'anitialiasing', obtaining a more precise split
         //       by f. ex. subdividing cells cut by the split depths.
@@ -61,6 +63,7 @@ namespace Opm
                 }
             }
         }
+#pragma clang diagnostic pop
 
         enum WaterInit { WaterBelow, WaterAbove };