[CFT] libelf/libdwarf import and ctfconvert update

[Kai Wang]

Hi list,

As some of you might already know, I'm working on integrating new
versions of libelf and libdwarf from elftoolchain project back to
FreeBSD and updating the ctfconvert tool for Clang 3.4 import.

The patch is available below and applies to head at r260988: (It could
be applied/tested together with dim@'s Clang 3.4 patch)

  http://people.freebsd.org/~kaiw/head-r260988-libdwarf-libelf-ctfconvert.diff.gz

Tests/reviews/comments are appreciated!


A short changelog:

* libelf and libdwarf in base is replaced by their counterparts in
  elftoolchain. The elftoolchain versions of these libraries
  originated from FreeBSD and have being maintained and furthur
  developed outside of FreeBSD source tree.
* The new version of libelf includes a few new APIs and numerous bug
  fixes (some of them have been merged back in the past years)
* The new version of libdwarf is based on jb@'s libdwarf in our src/
  tree and has support for dwarf call frame, line number info, among
  other things. Currently it supports reading DWARF[23] and partial
  DWARF4, and writing DWARF2. The APIs are 99% compatible with the LGPL
  libdwarf and are fully documented. Some of incompatible APIs from
  jb@'s libdwarf are kept as our own extensions.
* The ctfconvert tool is updated to use the API from the new libdwarf.
  Improvements were made so it can properly read/process dwarf info
  generated by Clang 3.4. (see r260880 and r260897 for details)


Thanks,
Kai