Unbeknownst to me the Swift LLDB branch already had an almost identical
API with this name, so it makes sense to merge the two.

This is motivated by exposing some Swift language-specific flags through
the API, in the example here it is used to communicate the Objective-C
runtime version. This could also be a meaningful extension point to get
information about "embedded: languages, such as extracting the C++
version in an Objective-C++ frame or something along those lines.

This reverts commit fbaf48be0ff6fb24b9aa8fe9c2284fe88a8798dd.

This has broken all LLDB buildbots:
https://lab.llvm.org/buildbot/#/builders/68/builds/44990
https://lab.llvm.org/buildbot/#/builders/96/builds/33160

Removing .c_str() has a semantics difference, but the use scenarios
likely do not matter as we don't have NUL in the strings.

Applied modernize-use-default-member-init clang-tidy check over LLDB.
It appears in many files we had already switched to in class member init but
never updated the constructors to reflect that. This check is already present in
the lldb/.clang-tidy config.

Differential Revision: https://reviews.llvm.org/D121481

When debugging LanguageRuntime unwindplans, it can be
helpful to disable their use and see the normal
stack walk.  Add a setting for this.

Differential Revision: https://reviews.llvm.org/D99828

Add calls into LanguageRuntime when finding the unwind method to
use out of the 0th (currently executing) stack frame.

Allow for the LanguageRuntimes to indicate if this stack frames
should be treated like a zeroth-frame -- symbolication should be
done based on the saved pc address, not decremented like normal ABI
function calls.

Add methods to RegisterContext and StackFrame to get a pc value
suitable for symbolication, to reduce the number of places in lldb
where we decrement the saved pc values before symbolication.

<rdar://problem/70398009>
Differential Revision: https://reviews.llvm.org/D97644

Add a facility in the LanguageRuntime to provide a special
UnwindPlan based on the register values in a RegisterContext,
instead of using the return-pc to find a function and use its
normal UnwindPlans.

Needed when the runtime has special stack frames that we want
to show the user, but aren't actually on the real stack.
Specifically for Swift asynchronous functions.

With feedback from Greg Clayton, Jonas Devlieghere, Dave Lee

<rdar://problem/70398009>

Differential Revision: https://reviews.llvm.org/D96839

This is a polymorphic class, copying it is a bad idea.

This was not a problem because most classes inheriting from it were
deleting their copy operations themselves. However, this enables us to
delete those explicit deletions, and ensure noone forgets to add them in
the future.

LangaugeRuntime and SystemRuntime now both inherit from Runtime.