[RFA] Revised C++ ABI abstraction patches

[Michael Elizabeth Chastain]

Lightly proofread, no obvious errors found.

I would prefer constructor_prefix_p et al to be real functions rather
than macros.  When I single-step code in gdb, it's a lot easier to follow
real functions than macros.

If I get some bandwidth I'll test it against gcc 2.95.2 and gcc-3pre
on a Solaris machine.

Michael