Revert "[TargetRegisterInfo] Refactor the code to use BitMaskClassIterator."
Revert "[TargetRegisterInfo] Refactor the code to use BitMaskClassIterator."

This reverts commit r265734.
Looks like ASan is not happy about it.
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/11741

Looking.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@265755 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm