IPA-ref infrastructure and WPA partitioning

[Jan Hubicka]

> Hi,
> as I noticed with some other testing, xalanbmk breaks with the patch with -O2
> (but not with -O3).  This is latent issue in symtab merging related to fact
> that we no longer stream unnecesary varpool nodes that affect the
> prevailability.  SPEC tester seem to get same ICE at -O3 and couple extra
> flags, but to reduce dependencies, here is patch with extra loop ensuring that
> we still save all varpool nodes to every output file.  This is very ineffecient
> for WHOPR, but otherwise it is not too bad.
^^ and same as we do currently. (one of points of reference streaming is to fix
the whopr partitioning issues)

Honza