[MachineOutliner] Test for X86FI->getUsesRedZone() as well as Attribute::NoRedZone

This commit is similar to r329120, but uses the existing getUsesRedZone() function
in X86MachineFunctionInfo. This teaches the outliner to look at whether or not a
function *truly* uses a redzone instead of just the noredzone attribute on a
function.

Thus, after this commit, it's possible to outline from x86 without using
-mno-red-zone and still get outlining results.

This also adds a new test for the new redzone behaviour.

llvm-svn: 329134