Plugify Objective-C++ parser bits

[Joseph S. Myers]

Note further that we support builds from gcc-core plus gcc-g++ tarballs - 
while the separate tarballs probably don't make much sense now, as long as 
it is supported you can't make files in gcc/cp depend on those in 
gcc/objcp.

Making Obj-C++ a runtime-conditional mode of the C++ compiler (and Obj-C 
of the C compiler, with the code in objc/ built just once like that in 
c-family/) would seem to me to be a better direction than the general 
direction of this patch series.  Remember the aim to separate interface 
and implementation, with fewer macros and inline functions and consequent 
greater importance of being able to link the compiler with LTO, which 
makes it desirable not to link so many different versions of the compiler 
for different languages....

-- 
Joseph S. Myers
joseph@codesourcery.com