[MachineOutliner] Keep track of fns that use a redzone in AArch64FunctionInfo

This patch adds a hasRedZone() function to AArch64MachineFunctionInfo. It
returns true if the function is known to use a redzone, false if it is known
to not use a redzone, and no value otherwise.

This removes the requirement to pass -mno-red-zone when outlining for AArch64.

https://reviews.llvm.org/D45189

llvm-svn: 329120