These are just FXSAVE and FXRSTOR with REX.W prefixes. These versions use
64-bit pointer values instead of 32-bit pointer values in the memory map they
dump and restore.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125446 91177308-0d34-0410-b5e6-96231b3b80d8