Getting Apple's libstdc++ debug mode into the FSF tree

[snyder]

>>>>> "Nathan" == Nathan Myers <ncm-nospam@cantrip.org> writes:
    Nathan> checking by default.  Is there anybody reading who can say
    Nathan> more about how/why the decision was made, and/or what it
    Nathan> would take to get it revisited?

Well, i can say that we turned it off here because including the
concept checks increased the sizes of the object files by, IIRC,
~30% or so, due to the additional debugging information.

Now that the patch i submitted to eliminate unreferenced types from the
dwarf debugging output has gone into gcc, this problem should have
gone away (though i haven't actually tried turning concept checks
back on to verify it).
sss