Don't mark record decls invalid when one of its methods is invalid, PR18284.

Without this patch, record decls with invalid out-of-line method delcs would
sometimes be marked invalid, but not always.  With this patch, they are
consistently never marked invalid.

(The code to do this was added in
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20100809/033154.html
, but the test from that revision is still passing.)

As far as I can tell, this was the only place where a class was marked invalid
after its definition was complete.