Added the preprocessor macro Q_DECL_DEPRECATED_X

Added a macro to provide deprecation warnings with a custom text.  If
the compiler does not support the feature, it falls back to
Q_DECL_DEPRECATED instead.

Currently supports msvc, gcc, and clang.  The armcc documentation didn't
show that the feature was available.

Change-Id: Iebdb00738a135c756e032eb76152c405a8c29a45
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>