Insert crashing stack frame when call to null func ptr

On arm64 targets, when the crashing pc is 0, the caller
frame can be found by looking at $lr, but the crash
reports don't use that trick to show the actual crashing
frame.  This patch adds that stack frame that lldb shows.

Also fix an issue where some register names were printed
as having a prefix of 'None'.

Differential Revision: https://reviews.llvm.org/D125042
rdar://92631787