I am posting this patch mainly to support python-dev discussion on this 
topic.  In the past (see r45330) it was possible to compile python core 
and standard library modules using a C++ compiler.

According to Martin v. Löwis (issue4665), "It's not a requirement that 
the Python source code is compilable as C++. Only the header files 
should be thus compilable." However, I can see certain benefits from 
such requirement:

1. It is hard to verify that header files are compilable if source code 
is not.  With compilable source code, CC=g++ ./configure; make will 
supply an adequate test that does not require anything beyond a standard 
distribution.

2. Arguably, C++ compliant code is more consistent and less error prone.   
For example, "new" is a really bad choice for a variable name regardless 
of being a C++ keyword, especially when used instead of prevailing "res" 
for a result of a function producing a PyObject. Even clearly redundant 
explicit casts of malloc return values arguably improve readability by 
reminding the type of the object that is being allocated.

3. Compiling with C++ may reveal actual coding errors that otherwise go unnoticed.  For example, use of undefined PyLong_BASE_TWODIGITS_TYPE in Objects/longobject.c.

4. Stricter type checking may promote use of specific types instead of 
void* which in turn may help optimizing compilers.

5. Once achieved, C++ compilability is not that hard to maintain, but 
restoring it with patches like this one is hard because it requires 
review of changes to many unrelated files.