Renaming GCC_ATTR

[Rik]

1/3/16

jwe,

You suggested moving to a more generic naming scheme since the NORETURN and
DEPRECATED attributes may no longer be GCC specific if they are implemented
through the C++ 2011 standard.  The obvious path would be to move to
OCTAVE_ATTR_NORETURN and OCTAVE_ATTR_DEPRECATED.  However, both these names
are really, really long.  Would OCTAVE_DEPRECATED and OCTAVE_NORETURN be
acceptable?

Also, what about OCTAVE_API?  This is really a __declspec which only exists
for Windows.  Is there a clearer name we could use?  Maybe OCTAVE_WINAPI?

--Rik