The former is deprecated with C++14. The standard says both are the same:

The contents and meaning of the header<cstddef>are the same as the C
standard library header<stddef.h>,except that it does not declare the type
wchar_t, that it also declares the type byte and its associated
operations (21.2.5), and as noted in 21.2.3 and 21.2.4.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The result shall be positive.

We can remove those C++11 and C++14 kludges because we require GCC 4.9
now.

Replaces GLib's GError.

Look up top-level config options by enum (= integer), not by name
string.