[cfe-dev] Make standalone-debug default based on glldb tuning

[David Blaikie via cfe-dev]

I realized recently (as folks at Google have started experimenting
with LLDB) that the platform default for debugger tuning and the
default for -fstandalone-debug are both independent. This seems a bit
wrong to me because enabling -glldb doesn't enable -fstandalone-debug.

I'm wondering if everyone's on board with removing
ToolChain::GetDefaultStandaloneDebug, and using
ToolChain::getDefaultDebuggerTuning() to select the default standalone
debug state?

Then on the command line, I'd kind of expect one to override the
other, so things like "-glldb -fno-standalone-debug" is respected
(when it comes to hopefully fixing LLDB to cope with standalone debug
input).

Sound good to everyone? If so I'll make a patch & send it for review.
(well, I'll probably work on the patch now anyway)

- Dave