branch for PCH GC work

[Geoff Keating]

The first step in merging the PCH work into current FSF GCC is to
integrate the garbage collection changes.  This is likely to cause
quite a bit of instability, so I'm about to create a branch off the
head of the CVS tree in which to hold this work, called pchgc-branch.

Once this part is done and integrated back into the tree, the
remaining PCH work should be able to be done in the mainline.

-- 
- Geoffrey Keating <geoffk@geoffk.org>