Lldb support code for mono (#4225)

Lldb support code for mono (#4225)

* Initial version of lldb support code.

* [lldb] Keep all the debug entries in a linked list so lldb can read it after attaching to the process.

* [lldb] Add an --enable-minimal=lldb option to disable the code. Add locking.

* [lldb] Add support for dynamic methods by adding a new protocol entry for unloading code regions.

* [lldb] Add beginnings of a test suite using the lldb python bindings.

* [lldb] Emit line number info for methods, not used yet.

* [lldb] Add dummy fields to structures to make sure 64 bit fields are 64 bit aligned.

* [lldb] Finish emission of line number info.

* [lldb] Use mono_method_full_name () for computing method names.

* [lldb] Emit info for specific trampolines as well.

* [lldb] Add tests for line number info.

* [lldb] Fix unwind info encoding on x86.

* [lldb] Skip seq points with no native offset.

* [lldb] Add tests for breakpoints.