Avoid use of "register" as optimization hint

[Roland McGrath]

> This topic came up when I wanted to use more recent GMP sparc code in
> glibc's sysdeps, and I ended up only being able to use code that I had
> written completely myself.
> 
> Others, at the time, did not express the same level of confidence you do.

Do you mean just others here, or did you ask a GMP maintainer and/or an FSF
licensing representative?