dev-lang/ghc-7+: ia64: add optimize-for-size to try to rebuild binaries

It did not work as-is for ghc-7.0.4-stage2.
It linked something, but didn't manage to
handle signals (died on handler).

Needs to be investigated and fixed.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>