[cfi] Cross-DSO CFI diagnostic mode (clang part)

* Runtime diagnostic data for cfi-icall changed to match the rest of
  cfi checks
* Layout of all CFI diagnostic data changed to put Kind at the
  beginning. There is no ABI stability promise yet.
* Call cfi_slowpath_diag instead of cfi_slowpath when needed.
* Emit __cfi_check_fail function, which dispatches a CFI check
  faliure according to trap/recover settings of the current module.
* A tiny driver change to match the way the new handlers are done in
  compiler-rt.

llvm-svn: 258745