As of today we only use .cfi_offset to specify the offset of a CSR, but
we never use .cfi_restore when the CSR is restored.
If we want to perform a more advanced type of shrink-wrapping, we need
to use .cfi_restore in order to switch the CFI state between blocks.
This patch only aims at adding support for the directive.
Differential Revision: https://reviews.llvm.org/D36114
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317199 91177308-0d34-0410-b5e6-96231b3b80d8