Move new totalorder from libm to libc

[Gabriel F. T. Gomes]

On Sat, 14 Dec 2019, Florian Weimer wrote:

>Should we define the new totalorder in libc, so that it is harder to
>get the wrong version at run time due to underlinking?

I didn't understand how underlinking could cause a wrong version to be
selected.  Isn't totalorder only provided by libm?  Where would a user
program get the old version from?  I can only imagine it getting undefined
references during link time.