[m-rev.] for-review: Apply upstream BoehmGC changes for glibc lock elision bug workaround

[Julien Fischer]

Hi,

On Thu, 16 Oct 2014, Paul Bone wrote:

> Do you still want to test this or shall I commit it?  I've heard no
> complaints from Boehm GC people about these changes.

I still haven't had time to test this, but think you should go ahead
and commit anyway.  I'll try to take a look once the changes make
there way into the rotds.

Cheers,
Julien.