I'm not speaking for Apple here, and I am not a lawyer. However, the
last draft of the runtime library exception clause (which is quite
old
by now) imposed licensing restrictions on the executables generated
by
GCC (due to linked runtime libraries) if you did certain things to
the
compiler. I'm personally very eager to see the final wording,
because
the draft I saw (again, which is old and has certainly changed) was
extremely aggressive.
I do not know what draft you saw, but I don't think I ever saw it,
unless we disagree on the meaning of "extremely aggressive."
In the general sense, you are most likely correct: if you modify gcc
by adding GPL-incompatible software used to generate code, it is
likely that you will not be granted any exception to the GPL when
using the runtime library. In other words, if you 1) add an
optimization pass to gcc using the (hypothetical) plugin architecture,
and 2) that optimization pass is not licensed under a GPL-compatible
license, and 3) you generate object code using that optimization pass,
and 4) you link that generated object code with the gcc runtime
library (e.g., libgcc or libstdc++-v3), then you will not be permitted
to distribute the resulting executable except under the terms of the
GPL.