MIsched: add an ILP window property to machine model.
MIsched: add an ILP window property to machine model.

This was an experimental option, but needs to be defined
per-target. e.g. PPC A2 needs to aggressively hide latency.

I converted some in-order scheduling tests to A2. Hal is working on
more test cases.

git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@171946 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx