Add data race detector plugin

[AlphaDaze]

This PR adds a data race detector plugin. This plugin detects possible data races within the underlying program along with information that can be utilised for debugging.

The README provides further context for the plugin and its usage.

Compile with make datarace_ft and run with mambo_datarace_ft. The plugin includes two algorithms which can be compiled separately: fasttrack and djit. Both are happens-before algorithms with fasttrack being an improvement over djit with both memory and runtime.

All comments and suggestions are welcome!

Sample output

--- FORK: Thread 1029188 created by 0
--- LOCK: Thread 1029188 locked 0x7fff22128b10
--- UNLOCK: Thread 1029188 unlocked 0x7fff22128b10
--- FORK: Thread 1029189 created by 1029188
--- LOCK: Thread 1029188 locked 0x7fff22128b10
--- UNLOCK: Thread 1029188 unlocked 0x7fff22128b10
--- FORK: Thread 1029223 created by 1029188
--- JOIN: Thread 1029189 joining 1029188
!!! READ RACE: Possible read race - 0x41104c by thread 1029223
>>>> at 0x40074c: /home/user/Documents/git/tests/hg04_race (0x400744) (th10)
!!! WRITE RACE: Possible write race - 0x41104c by thread 1029223
>>>> at 0x40075c: /home/user/Documents/git/tests/hg04_race (0x400744) (th10)
--- JOIN: Thread 1029223 joining 1029188
--- LOCK: Thread 1029188 locked 0x7fff22128ab0
--- UNLOCK: Thread 1029188 unlocked 0x7fff22128ab0
We're done; exiting with status: 0

[IgWod]

Hi @AlphaDaze,

Thank you for your contribution. It looks good, however there are few things I'd like to be addressed before merging it. Please see attached comments.

Also, a major point, please remove any commented out code or add explanation why it's commend out and how it can be used in the future. We don't need any dead code in the repo :).

Let me know if something is unclear.

Many thanks,
Igor

[IgWod]

Thanks for addressing the comments. I found two more small issues, but I'm happy otherwise. Please either remove the commented out code I highlighted or add TODO/explanation why it's commented out.

The other things is commit messages. Could you please clean it up? Ideally we would like to have two commits. The first commit for changes to the core and then the second one adding the plugin. Shouldn't be too difficult to achieve with git rebase -i and some amending.

Once that's done I'm happy with the PR, but I'll ask @jkressel to have a look as well, and once he approves it we can merge it.

[AlphaDaze]

Sounds good! Thanks for taking a look at it. I have rebased and squashed the relevant commits together as requested.

If there is any other changes (however small), please do let me know.

[josh-nook]

Looks good to me (I'm a new intern). The markdown reads well

[IgWod]

Looks good to me! I'll ask @jkressel to have a look now.

[jkressel]

Looks good to me, I'm happy to merge.