[m-dev.] Upgrading Boehm GC, attempt #2

[Paul Bone]

Update:

I've merged master into my branch and found that I can build and bootcheck
in asm_fast.gc, but I have a testcase failure.

hard_coded/tl_backjump_test

    Mercury runtime: memory zone nondetstack#2 overflowed
    This may have been caused by a stack overflow, due to unbounded recursion.

I'm working on this but I can't immediately see how GC affects thread-local
backjumping.  But I guess that's the nature of GC *shrug*.  Anyway if anyone
has a clue that'd help, I'll keep working on it.

Cheers.


-- 
Paul Bone