LLDB on FreeBSD/arm64 and arm

[Ed Maste]

As you may know, the FreeBSD Foundation sponsored Moritz Systems to
improve LLDB's support of non-x86 FreeBSD targets (and some other
improvements applicable to all targets). This builds on their earlier
work to update x86 support.

Initial changes for arm64 and arm support were recently committed
upstream. Details are in these code reviews, if you're interested:

https://reviews.llvm.org/D95297 (arm64)
https://reviews.llvm.org/D95696 (arm)

arm and arm64 users with an interest in LLDB are encouraged to build
LLDB from the upstream git repository, try out the support, and report
issues or positive results.

It should build using the regular build process as described at
https://lldb.llvm.org/resources/build.html

At present all four of 32- and 64-bit arm and x86 use LLDB's
non-legacy debug support by default. Legacy support will be removed
from LLDB upon completion of Moritz' work (once all architectures are
patched) and there is no need to try out legacy support.