toolchain: gcc: add __DEPRECATED_MACRO

Add a macro which signals to the compiler that use of the macro is
deprecated.

Example:

  #define FOO __DEPRECATED_MACRO bar

Defines FOO to 'bar' but emits a warning if used in code.

Cannot filter out with -Wno-deprecated, so be careful with -Werror.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>