problem with your GIMPLE_FORMAL_TEMP change

[Richard Kenner]

    Need some way to notice when we've made the substitution.  If you've
    got SAVE_EXPR< VAR_DECL <x> >, and X is a variable that might change,
    we do still need to copy the value to a new temporary.

OK, right.

    I'm now thinking that we should have a bit on the SAVE_EXPR itself
    to notice when it has been resolved.

Why clear DECL_GIMPLE_FORMAL_TEMP_P when leaving a context?  Not doing
that would also fix this, but I'm not sure what it might break since I
don't understand why its being cleared.