[Layout] Add a new option (NFC)

Currently cost based loop rotation algo can only be turned on with
two conditions: the function has real profile data, and -precise-rotation-cost
flag is turned on. This is not convenient for developers to experiment
when profile is not available. Add a new option to force the new
rotation algorithm -force-precise-rotation-cost




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269266 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed