[Bug c++/71919] New: Redefinition of user-defined conversions (via typedef) shouldn't compile

["jmgao at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71919

            Bug ID: 71919
           Summary: Redefinition of user-defined conversions (via typedef)
                    shouldn't compile
           Product: gcc
           Version: 6.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jmgao at google dot com
  Target Milestone: ---

GCC does not emit an error (or warning) when two user-defined conversion
functions are defined inline with the same type via typedef. When one or more
of the functions don't have inline definitions, an error happens as expected.

Example (also at https://godbolt.org/g/YYOqja):
  typedef int foo;
  struct bar {
    operator int() { return 0; }
    operator foo() { return 0; }
  };