Merge libcxxrt commit 5d8a15823a103bbc27f1bfdcf2b5aa008fab57dd

Merge libcxxrt commit 5d8a15823a103bbc27f1bfdcf2b5aa008fab57dd

  Fix two bugs in __cxa_end_cleanup()

  Per the EHABI32 specification, __cxa_end_cleanup must take care to
  preserve registers before calling _Unwind_Resume().  So, libcxxrt uses
  an assembly stub which preserves caller-saved registers around the call
  to __cxa_get_cleanup().  But:
  - it failed to restore them properly,
  - it did not preserve the link register.

  Fix both of these problems.  This is needed to fix exception unwinding
  on FreeBSD with LLVM 14.  Note that r4 is callee-saved but is pushed
  onto the stack to preserve stack pointer alignment.

  Sponsored-by: The FreeBSD Foundation
MFC after:	1 week