possible to adjust OPTIONS_DEFAULT based on COMPILER_TYPE?

[Don Lewis]

I've run into a situation where I'd like to change OPTIONS_DEFAULT based
on the value of the value of COMPILER_TYPE.  I'm setting USE_GCC=yes. If
the base compiler is gcc, then I can enable a particular option to make
the port more featureful.  If the base compiler is clang, then some of
the other ports the option depends on are C++ code that gets compiled
with clang and the port breaks because of the libstdc++ vs. libc++
conflict.  In that case, I'd like to disable the option to at least have
working binary packages available, even though they aren't as
featureful.

This doesn't look possible, though.  OPTIONS_DEFAULT needs to be set
before the .include <bsd.port.options.mk>, and COMPILER_TYPE isn't set
until after that, or possibly even after bsd.port.pre.mk.