The C and C++ standards say it's undefined whether the preprocessor
supports macros that expand to defined() will operate as an ifdef.
Clang 3.9 started complaining about that fact.

One solution was to change QT_SUPPORTS to check for zero or one, which
means we need to change the #defines QT_NO_xxx to #define QT_NO_xxx 1.
The C standard says we don't need to #define to 0, as an unknown token
is interpreted as zero. However, that might produce a warning (GCC with
-Wundef), so changing the macro this way is not recommended.

Instead, we deprecate the macro and replace the uses with #ifdef/ndef.

Change-Id: Id75834dab9ed466e94c7ffff1444874d5680b96a
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>