[PATCH] Fix C++ debug tests

[Joseph Myers]

On Thu, 9 Feb 2017, Wilco Dijkstra wrote:

> The internal header include/string.h does not work in C++: it causes 
> link errors in several C++ debug tests when any of the functions it 
> declares are called. The best option would be to not use internal 
> headers for tests (unless explicitly needed).  As a workaround for now, 
> add extern "C" {} to the C++ debug tests.

I think extern "C" belongs around specific declarations in headers, not 
around whole source files.  I'd suggest disabling the internal 
declarations if __cplusplus instead (just as they are disabled for 
_ISOMAC).

-- 
Joseph S. Myers
joseph@codesourcery.com