In r268475 I made a change to ObjectFileMachO so that if it is

missing an LC_FUNCTION_STARTS section, we assume it has been
aggressively stripped (it is *very* unusual for anyone to strip
LC_FUNCTION_STARTS) so we disable assembly instruction unwind plan
creation.

Kernel extensions (kexts) don't have LC_FUNCTION_STARTS, but we
almost always have good symbol bounds just with the linker symbols.
So add an exception to allow assembly instruction unwind plan
creation for kexts even though they lack LC_FUNCTION_STARTS.

<rdar://problem/26453952> 

llvm-svn: 270618