Improve disable-language-runtime-unwindplans description to be more searchable

[jasonmolenda]

Summary

The current description for "disable-language-runtime-unwindplans" can only be found with apropos by searching for backtracing. It should be discoverable with terms like stack and backtrace. I'm also not thrilled with my mention of "LanguageRuntime" here, because no one outside lldb developers would know what that means. Maybe this is a little better. Open to suggestions.

lldb/source/Target/TargetProperties.td

     Desc<"A path to a python OS plug-in module file that contains a OperatingSystemPlugIn class.">;
   def StopOnSharedLibraryEvents: Property<"stop-on-sharedlibrary-events", "Boolean">,
     Global,
     DefaultFalse,
     Desc<"If true, stop when a shared library is loaded or unloaded.">;
   def DisableLangRuntimeUnwindPlans: Property<"disable-language-runtime-unwindplans", "Boolean">,
     Global,
     DefaultFalse,
-    Desc<"If true, LanguageRuntime plugins' UnwindPlans will not be used when backtracing.">;
+    Desc<"If true, language runtime augmented/overidden backtraces will not be used when printing a stack trace.">;
   def DetachKeepsStopped: Property<"detach-keeps-stopped", "Boolean">,
     Global,
     DefaultFalse,
     Desc<"If true, detach will attempt to keep the process stopped.">;
   def MemCacheLineSize: Property<"memory-cache-line-size", "UInt64">,
     DefaultUnsignedValue<512>,
     Desc<"The memory cache line size">;
   def WarningOptimization: Property<"optimization-warnings", "Boolean">,