[llvm] r235988 - Use CIE version 4 for dwarf4.

[Robinson, Paul]

> > So although the version number in the CIE is now 4 for dwarf-4, the 2
> new
> > fields expected in a dwarf-4 CIE header are currently missing.
> And this breaks the debug info everywhere, right?

Each section (more-or-less) has its own version number, so this would break
only the interpretation of the frame section.

My reading of the standards is that if the section is named .debug_frame
then its content is defined by the DWARF standard. If .debug_frame has
version=4 then it needs the new fields to conform.

If the section is named .eh_frame then its content is defined by the ABI,
which arguably requires it to use the DWARF 2 format. But if you emit a
.eh_frame section with version=4 then it should use DWARF 4 format as well.
But I think it is not guaranteed that all relevant software will understand
.eh_frame with version=4.
--paulr