re PR go/78763 (go1: internal compiler error: in do_get_backend, at go/gofrontend/expressions.cc:8352)

	PR go/78763
    compiler: call determine_types even for constant expressions
    
    We need to call determine_types even for constant expressions, since a
    constant expression may include code like unsafe.Sizeof(0).  Something
    needs to determine the type of the untyped 0, and that should be the
    determine_types pass.
    
    Implementing that triggered a compiler crash on test/const1.go because
    it permitted some erroneous constants to make it all the way to the
    backend.  Catch that case by checking whether we get a constant
    overflow error, and marking the expression invalid if we do.  This is
    a good change in any case, as previously we reported the same constant
    overflow error multiple times, and now we only report it once.
    
    Fixes GCC PR 78763.
    
    Reviewed-on: https://go-review.googlesource.com/34496

From-SVN: r243729