What mac osx version do you have?
Actually, it looks like it is finding the wrong version of the "strip" executable. If you do "which strip" from a terminal it should tell you.
You can override this be setting the HXCPP_STRIP variable, bit I don't have my mac, so I'm not sure what is should be.
You may also be able to hide (rename) the offending strip exe and let the system find the new one.
I wonder if the gcc toolchain should have something like:
<exe name="xcrun --sdk macosx${MACOSX_VER} strip" if="HXCPP_CLANG" />
Hugh