Merge LLDB plugin into master

Summary:
LLDB plugin is now working for basic debugging use cases.

Things that work:
- Basic execution control: start, continue, step etc.
- Break points
- Frame stack list
- Symbol info when hover
- Variables & Expressions (still have caveats)
- Multi-threaded debugee (must use LLDB trunk version)
- Debugger console
- Remote debugging (only tested on localhost)

Things not working yet:
- Disassembly/Register view
- Memory view
- Pending break points and anything requires pending break points
- Watch points
- Attach to process (works internally, no UI to access it)

Not tested:
- Examine core file
- Drkonqi support

There's a `debugers/lldb/TODO.txt` which contains more detailed description of current limitations and link to related LLDB bug reports.

Note: the whole thing might crash from time to time without [this bug](https://llvm.org/bugs/show_bug.cgi?id=28026) fixed. I'm using LLDB built myself with the code fixed. The patch can be found in the bug report.

Test Plan:
- GDB unit tests (such that I didn't break anything)
- LLDB unit tests (some of them are skipped due to limitations mentioned above)
- Manually tested

Reviewers: apol, #kdevelop

Reviewed By: apol, #kdevelop

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D2293