[cxx-mem-model] testing infrastructure

[Aldy Hernandez <aldyh at redhat dot com>]

Hi folks.

The following is a test harness for testing atomicity problems and data 
races in multi-threaded environments.  Please see the README file in the 
patch below, which describes the use of GDB to test in-between states in 
a possibly threaded execution.

I would like to use this branch as the repository for tests of data 
races introduced by the compiler (atomics, illegal memory hoists of 
global variables in a multi-threaded environment, etc etc).

Eventually, as part of this project, I will be adding flags to the 
compiler (-fno-allow-load-data-races, etc), which we can use to safe 
guard against these illegal data race injections by the compiler.  Until 
then, I expect all (or most) of the tests below to fail.

A few tidbits...

1. I stole the GDB checks in the guality harness to check the presence 
of GDB.  If there is a more canonical way of checking the presence of a 
working gdb, let me know.

2. There is a README explaining the infrastructure, and the anatomy of a 
test.

3. Most of this work is actually Andrew Macleod's, who is off in a 
tropical island somewhere.  I have stolen most of his tests, implemented 
the harness, and cleaned up things for submission.  All errors, are 
obviously mine.

I would appreciate comments, and/or new relevant tests/problems you have 
encountered and would like fixed in the future.  I know there are a few 
Linux kernel problems that fall into this category.

Fire away, I don't mind being crucified.
Aldy

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