maint: Rename attributes GCC_ATTR_XXX to OCTAVE_XXX. * oct-conf-post.in.h: Rename macros GCC_ATTR_XXX to OCTAVE_XXX. Add comments describing purpose of macros. Add FIXME note about switching macros to C++ standard convention. Add FIXME note about using visibility attributes. * error.cc, error.h, gripes.h, jit-typeinfo.cc, load-save.cc, oct-stream.cc, pt-jit.cc, symtab.h, variables.h, ov-base-sparse.h, ov-base.cc, ov-base.h, ov-class.cc, ov-classdef.cc, ov-classdef.h, ov.cc, ov.h, octave.cc, pt-mat.cc, Array.h, DiagArray2.h, PermMatrix.h, Range.h, Sparse.h, dSparse.h, f77-fcn.h, lo-error.c, lo-error.h, quit.h, SparseCmplxQR.cc, lo-array-gripes.h, unwind-prot.h: Rename attributes GCC_ATTR_XXX to OCTAVE_XXX.

--- a/libinterp/parse-tree/pt-mat.cc	Tue Jan 05 13:04:02 2016 -0800
+++ b/libinterp/parse-tree/pt-mat.cc	Tue Jan 05 14:16:58 2016 -0800
@@ -273,7 +273,7 @@
   return retval;
 }
 
-GCC_ATTR_NORETURN static
+OCTAVE_NORETURN static
 void
 eval_error (const char *msg, const dim_vector& x, const dim_vector& y)
 {