--enable-build-with-cxx vs plugins (Was: Re: Extra regressions for --enable-build-with-cxx)

[Joern Rennecke]

Quoting Ian Lance Taylor <iant@google.com>:

> I'm not surprised that plugins don't work

For Milepost we need both the --enable-build-with-cxx configure option
and plugins.
How is this supposed to work?
Should the person compiling the plugins use C++ to compile the plugin?
Or should the cc1 / cc1plus dso export unambiguous symbols with C linkage
names in addition to the C++ linkage names?
Or should we have a language extension to specify C++ linkage in C headers,
and arrange for the gcc headers that are installed for teh benefit of plugins
to reflect the used build/bootstrap language so that either gcc or g++ will
just work, using references with the appropriate names?