While reviewing [basic.scope.param] I noticed we don't show the location
of the previous declaration when giving an error about "A parameter name
shall not be redeclared in the outermost block of the function definition".
PR c++/94588
* name-lookup.c (check_local_shadow): Add an inform call.
* g++.dg/diagnostic/redeclaration-1.C: Add dg-message.
