RFC/Ada: removal of $(ADAC) support

[Richard Kenner]

    The systems under discussion ship a "gnatgcc" based on GCC 2.8, but a
    "gcc" based on GCC 2.9x.  This was done for very good reason, that GCC
    2.8 worked fine for Ada but silently miscompiled C source code on at
    least one architecture that that system supports.  Second-guessing the
    system integrator in that scenario, by forcing CC to gnatgcc, would
    raise the risk of bootstrap failure due to a bug in the host compiler.

This isn't something we have to "guess" about.  Has anybody tried the
experiment of bootstrapping starting with that compiler? 

It seems likely it would work since lots of people bootstrapped GCC
starting with 2.8.1.