Add more proper C++ compilation support to distutils by
propagating information on used language to compiler as
well as linker. The information is used by
unixccompiler, cygwinccompiler and emxccompiler to call
a C++ compiler instead of a C compiler. Options for the
call are formed by as a union of options to both C and
C++ compilers.

The old version worked by accident on some platforms
where you can compile C++ programs by calling the C
compiler (e.g. gcc), but not on others (e.g. Tru64
Unix, probably also others not using gcc).

The more compilcated handling of options than with
linker is necessary to properly support manual
overrides such as "CXX=g++ -foo".

The attached patch is against CVS HEAD, but applies
with minimal changes at least to Python 2.3.