This patchs adds an optional warning that is printed when stopped at a
frame that was compiled in a source language that LLDB has no plugin
for.
The motivational use-case is debugging Swift code on Linux. When the
user accidentally invokes the system LLDB that was built without the
Swift plugin, it is very much non-obvious why debugging doesnt
work. This warning makes it easy to figure out what went wrong.
<rdar://problem/56986569>
Adrian Prantl