Change the ordering that we search for kexts and kernels on the local

computer.  When doing kernel debugging, lldb scrapes around a few 
well-known locations to find kexts and kernels.  It builds up two
lists - kexts and kernels with dSYM, and kexts and kernels without dSYMs.
After both lists have failed to provide a file, then we'll call out
to things like the DebugSymbols framework to find a kext/kernel.

This meant that when you had a kext/kernel on the local computer that
did not have debug information, lldb wouldn't consult DebugSymbols etc
once it'd locked on to one of these no-debug-info binaries on the local
computer.

Reorder this so we give DebugSymbols etc a shot at finding a debug-info
file before we use any of the no-debug-info binaries that were found on
the system.

<rdar://problem/34434440> 

llvm-svn: 320241