re PR go/67968 (go1: internal compiler error: in write_specific_type_functions, at go/gofrontend/types.cc:1812)

	PR go/67968
    compiler: Traverse types of call expressions.
    
    https://gcc.gnu.org/PR67968 provides a test case that causes a gccgo
    crash on valid code.  The compiler failed to build the hash and equality
    functions required for a type descriptor.  The descriptor is for an
    unnamed type that is being returned by a function imported from a
    different package.  The unnamed type is being implicitly converted to an
    interface type by a return statement.  The fix is to ensure that the
    type of a call expression is always traversed.
    
    Test case sent out for the master testsuite as
    https://golang.org/cl/16532 .

From-SVN: r229642