--std vs __intN

[DJ Delorie]

> N.B. almost all library macros are _GLIBCXX_XXX with only a single
> underscore at the beginning. If these are exported by the compiler
> then that might be a reason to use a different convention.

All the other macros being exported at that point in the compiler had
two underscores.

> .. but then maybe it shouldn't use "GLIBCXX" at all. Or maybe it
> should, I dunno :)

Now we're bikeshedding ;-)